ciao,puoi sempre prelevare il file winlogon dal cd di windows o da un altro computer con il floppy.
segui queste istruzioni qui---> http://www.p2pforum.it/forum/showthread.php?t=24378

poi avvia hijackthis,spunta sinistra su queste voci:
R1 - HKCU\Software\Microsoft\Internet Explorer\Main,Search Bar = http://www.couldnotfind.com/search_...count_id=145499
R1 - HKCU\Software\Microsoft\Internet Explorer\Main,Search Page = http://www.couldnotfind.com/search_...count_id=145499
R1 - HKCU\Software\Microsoft\Internet Explorer\Search,SearchAssistant = http://www.couldnotfind.com/search_...count_id=145499
R3 - URLSearchHook: (no name) - _{CFBFAE00-17A6-11D0-99CB-00C04FD64497} - (no file)
O8 - Extra context menu item: Web Rebates - file://C:\Programmi\Web_Rebates\Sy1150\Tp1150\scri1150a.h tm


e sotto su fix checked.