Ciao, anch'io ho avuto lo stesso problema la cpu passa dal 2% al 100% bloccando tutto.
A volte capita navigando, a volte usando nero, ma non c'è un programma in particolare che occupa tutta la memoria, ce ne sono di versi che occupano da 10.000 kb a 35.000 kb come mozilla, emule, explore.exe, svchost.exe ecc. ecc.
Cmq ti scrivo il risultato della scansione di hijack
Logfile of HijackThis v1.99.1
Scan saved at 20.03.10, on 11/11/2007
Platform: Windows XP SP2 (WinNT 5.01.2600)
MSIE: Internet Explorer v6.00 SP2 (6.00.2900.2180)

Running processes:
C:\WINDOWS\System32\smss.exe
C:\WINDOWS\system32\winlogon.exe
C:\WINDOWS\system32\services.exe
C:\WINDOWS\system32\lsass.exe
C:\WINDOWS\system32\svchost.exe
C:\WINDOWS\System32\svchost.exe
C:\WINDOWS\system32\LEXBCES.EXE
C:\WINDOWS\system32\spoolsv.exe
C:\WINDOWS\system32\LEXPPS.EXE
C:\WINDOWS\Explorer.EXE
C:\Programmi\Apoint2K\Apoint.exe
C:\WINDOWS\AGRSMMSG.exe
C:\Programmi\QuickTime\qttask.exe
C:\Programmi\HPQ\Quick Launch Buttons\EabServr.exe
C:\Programmi\Apoint2K\Apntex.exe
C:\Programmi\Java\j2re1.4.2_05\bin\jusched.exe
C:\PROGRA~1\Grisoft\AVGFRE~1\avgcc.exe
C:\Programmi\Lexmark X1100 Series\lxbkbmgr.exe
C:\Programmi\Zone Labs\ZoneAlarm\zlclient.exe
C:\Programmi\Lexmark X1100 Series\lxbkbmon.exe
C:\Programmi\Acronis\TrueImageHome\TimounterMonito r.exe
C:\Programmi\File comuni\Acronis\Schedule2\schedhlp.exe
C:\WINDOWS\system32\ctfmon.exe
C:\Programmi\File comuni\Ahead\lib\NMBgMonitor.exe
C:\Programmi\File comuni\Acronis\Schedule2\schedul2.exe
C:\PROGRA~1\Grisoft\AVGFRE~1\avgamsvr.exe
C:\PROGRA~1\Grisoft\AVGFRE~1\avgupsvc.exe
C:\PROGRA~1\Grisoft\AVGFRE~1\avgemc.exe
C:\WINDOWS\system32\gearsec.exe
C:\Programmi\Analog Devices\SoundMAX\SMAgent.exe
C:\WINDOWS\System32\svchost.exe
C:\WINDOWS\system32\ZoneLabs\vsmon.exe
C:\WINDOWS\system32\wscntfy.exe
C:\Programmi\Internet Explorer\iexplore.exe
C:\WINDOWS\system32\taskmgr.exe
C:\Programmi\File comuni\Microsoft Shared\Encarta Web Companion\2007\ENCWCSVR.EXE
C:\Program Files\HijackThis\HijackThis.exe

R1 - HKCU\Software\Microsoft\Internet Explorer\Main,Search Bar = http://ie.redirect.hp.com/svs/rdr?TY...lion&pf=laptop
R0 - HKCU\Software\Microsoft\Internet Explorer\Main,Start Page = http://ie.redirect.hp.com/svs/rdr?TY...lion&pf=laptop
R0 - HKCU\Software\Microsoft\Internet Explorer\Main,Local Page =
R0 - HKLM\Software\Microsoft\Internet Explorer\Main,Local Page =
R0 - HKCU\Software\Microsoft\Internet Explorer\Toolbar,LinksFolderName = Collegamenti
R3 - URLSearchHook: Yahoo! Toolbar con blocco Pop-Up - {EF99BD32-C1FB-11D2-892F-0090271D4F88} - C:\Programmi\Yahoo!\Companion\Installs\cpn\yt.dll
O2 - BHO: Yahoo! Toolbar Helper - {02478D38-C3F9-4EFB-9B51-7695ECA05670} - C:\Programmi\Yahoo!\Companion\Installs\cpn\yt.dll
O2 - BHO: AcroIEHlprObj Class - {06849E9F-C8D7-4D59-B87D-784B7D6BE0B3} - C:\Programmi\Adobe\Acrobat 6.0\Reader\ActiveX\AcroIEHelper.dll
O2 - BHO: (no name) - {53707962-6F74-2D53-2644-206D7942484F} - C:\PROGRA~1\SPYBOT~1\SDHelper.dll
O2 - BHO: Encarta Web Companion Oggetto helper - {955BE0B8-BC85-4CAF-856E-8E0D8B610560} - C:\Programmi\File comuni\Microsoft Shared\Encarta Web Companion\2007\ENCWCBAR.DLL
O3 - Toolbar: Yahoo! Toolbar con blocco Pop-Up - {EF99BD32-C1FB-11D2-892F-0090271D4F88} - C:\Programmi\Yahoo!\Companion\Installs\cpn\yt.dll
O3 - Toolbar: Encarta Web Companion - {147D6308-0614-4112-89B1-31402F9B82C4} - C:\Programmi\File comuni\Microsoft Shared\Encarta Web Companion\2007\ENCWCBAR.DLL
O4 - HKLM\..\Run: [Apoint] C:\Programmi\Apoint2K\Apoint.exe
O4 - HKLM\..\Run: [AGRSMMSG] AGRSMMSG.exe
O4 - HKLM\..\Run: [NvCplDaemon] "RUNDLL32.EXE" C:\WINDOWS\System32\NvCpl.dll,NvStartup
O4 - HKLM\..\Run: [nwiz] "nwiz.exe" /install
O4 - HKLM\..\Run: [Cpqset] "C:\Programmi\HPQ\Default Settings\cpqset.exe"
O4 - HKLM\..\Run: [QuickTime Task] "C:\Programmi\QuickTime\qttask.exe" -atboottime
O4 - HKLM\..\Run: [eabconfg.cpl] "C:\Programmi\HPQ\Quick Launch Buttons\EabServr.exe" /Start
O4 - HKLM\..\Run: [SunJavaUpdateSched] C:\Programmi\Java\j2re1.4.2_05\bin\jusched.exe
O4 - HKLM\..\Run: [AVG7_CC] "C:\PROGRA~1\Grisoft\AVGFRE~1\avgcc.exe" /STARTUP
O4 - HKLM\..\Run: [Lexmark X1100 Series] "C:\Programmi\Lexmark X1100 Series\lxbkbmgr.exe"
O4 - HKLM\..\Run: [ZoneAlarm Client] "C:\Programmi\Zone Labs\ZoneAlarm\zlclient.exe"
O4 - HKLM\..\Run: [AcronisTimounterMonitor] C:\Programmi\Acronis\TrueImageHome\TimounterMonito r.exe
O4 - HKLM\..\Run: [Acronis Scheduler2 Service] "C:\Programmi\File comuni\Acronis\Schedule2\schedhlp.exe"
O4 - HKCU\..\Run: [CTFMON.EXE] C:\WINDOWS\system32\ctfmon.exe
O4 - HKCU\..\Run: [MSMSGS] "C:\Programmi\Messenger\msmsgs.exe" /background
O4 - HKCU\..\Run: [BgMonitor_{79662E04-7C6C-4d9f-84C7-88D8A56B10AA}] "C:\Programmi\File comuni\Ahead\lib\NMBgMonitor.exe"
O4 - HKCU\..\Run: [E07IXLRD_20045015] "C:\Programmi\Microsoft Encarta\Microsoft Encarta 2007 - Premium DVD\EDICT.EXE" -m
O8 - Extra context menu item: E&sporta in Microsoft Excel - res://C:\PROGRA~1\MICROS~2\OFFICE11\EXCEL.EXE/3000
O9 - Extra button: (no name) - {08B0E5C0-4FCB-11CF-AAA5-00401C608501} - C:\WINDOWS\system32\msjava.dll
O9 - Extra 'Tools' menuitem: Sun Java Console - {08B0E5C0-4FCB-11CF-AAA5-00401C608501} - C:\WINDOWS\system32\msjava.dll
O9 - Extra button: (no name) - {85d1f590-48f4-11d9-9669-0800200c9a66} - %windir%\bdoscandel.exe (file missing)
O9 - Extra 'Tools' menuitem: Uninstall BitDefender Online Scanner v8 - {85d1f590-48f4-11d9-9669-0800200c9a66} - %windir%\bdoscandel.exe (file missing)
O9 - Extra button: Ricerche - {92780B25-18CC-41C8-B9BE-3C9C571A8263} - C:\PROGRA~1\MICROS~2\OFFICE11\REFIEBAR.DLL
O9 - Extra button: Barra di ricerca di Encarta - {B205A35E-1FC4-4CE3-818B-899DBBB3388C} - C:\Programmi\File comuni\Microsoft Shared\Encarta Search Bar\ENCSBAR.DLL
O9 - Extra button: Messenger - {FB5F1910-F110-11d2-BB9E-00C04F795683} - C:\Programmi\Messenger\msmsgs.exe
O9 - Extra 'Tools' menuitem: Windows Messenger - {FB5F1910-F110-11d2-BB9E-00C04F795683} - C:\Programmi\Messenger\msmsgs.exe
O16 - DPF: {0EB0E74A-2A76-4AB3-A7FB-9BD8C29F7F75} (CKAVWebScan Object) - http://www.kaspersky.com/kos/eng/par...an_unicode.cab
O16 - DPF: {193C772A-87BE-4B19-A7BB-445B226FE9A1} (ewidoOnlineScan Control) - http://downloads.ewido.net/ewidoOnlineScan.cab
O16 - DPF: {2BC66F54-93A8-11D3-BEB6-00105AA9B6AE} (Symantec AntiVirus scanner) - http://security.symantec.com/sscv6/S...in/AvSniff.cab
O16 - DPF: {5D86DDB5-BDF9-441B-9E9E-D4730F4EE499} (BDSCANONLINE Control) - http://download.bitdefender.com/reso...an8/oscan8.cab
O16 - DPF: {644E432F-49D3-41A1-8DD5-E099162EEEC5} (Symantec RuFSI Utility Class) - http://security.symantec.com/sscv6/S.../bin/cabsa.cab
O16 - DPF: {7B297BFD-85E4-4092-B2AF-16A91B2EA103} (WScanCtl Class) - http://www.ca.com/us/securityadvisor...fo/webscan.cab
O16 - DPF: {9A9307A0-7DA4-4DAF-B042-5009F29E09E1} (ActiveScan Installer Class) - http://acs.pandasoftware.com/actives...ree/asinst.cab
O16 - DPF: {BB21F850-63F4-4EC9-BF9D-565BD30C9AE9} (a-squared Scanner) - http://ax.emsisoft.com/asquared.cab
O16 - DPF: {E8F628B5-259A-4734-97EE-BA914D7BE941} (Driver Agent ActiveX Control) - http://driveragent.com/files/driveragent.cab
O17 - HKLM\System\CCS\Services\Tcpip\..\{DFD95687-4F7F-45DD-B6FC-E179AFFD1FD3}: NameServer = 85.37.17.49 85.38.28.91
O20 - Winlogon Notify: WgaLogon - C:\WINDOWS\
O23 - Service: Acronis Scheduler2 Service (AcrSch2Svc) - Acronis - C:\Programmi\File comuni\Acronis\Schedule2\schedul2.exe
O23 - Service: AVG7 Alert Manager Server (Avg7Alrt) - GRISOFT, s.r.o. - C:\PROGRA~1\Grisoft\AVGFRE~1\avgamsvr.exe
O23 - Service: AVG7 Update Service (Avg7UpdSvc) - GRISOFT, s.r.o. - C:\PROGRA~1\Grisoft\AVGFRE~1\avgupsvc.exe
O23 - Service: AVG E-mail Scanner (AVGEMS) - GRISOFT, s.r.o. - C:\PROGRA~1\Grisoft\AVGFRE~1\avgemc.exe
O23 - Service: gearsec - GEAR Software - C:\WINDOWS\system32\gearsec.exe
O23 - Service: HP WMI Interface (hpqwmi) - Hewlett-Packard Development Company, L.P. - C:\Programmi\HPQ\SHARED\HPQWMI.exe
O23 - Service: LexBce Server (LexBceS) - Lexmark International, Inc. - C:\WINDOWS\system32\LEXBCES.EXE
O23 - Service: NVIDIA Driver Helper Service (NVSvc) - NVIDIA Corporation - C:\WINDOWS\System32\nvsvc32.exe
O23 - Service: SoundMAX Agent Service (SoundMAX Agent Service (default)) - Analog Devices, Inc. - C:\Programmi\Analog Devices\SoundMAX\SMAgent.exe
O23 - Service: TrueVector Internet Monitor (vsmon) - Zone Labs, LLC - C:\WINDOWS\system32\ZoneLabs\vsmon.exe


Non credo che sia un problema di virus perchè ho fatto la scansione on line con almeno 5 antivirus diversi.
Vi sarei molto grato se mi aiutaste, non ne riesco proprio a venire a capo.
Inoltre guardando i forum questo della cpu è un probl molto diffuso...
grazie ancora....