se può interessare ho fatto alcune modifiche ed ho risolto:

if(RegOpenKeyEx(hReg,"System\\CurrentControlSet\\C ontrol\\ComputerName\\ComputerName",0,KEY_QUERY_VA LUE,&hReg)==ERROR_SUCCESS)
char *lpValue; DWORD tyValue=REG_SZ; DWORD cbValue;
oppure
TCHAR lpValue[100]; DWORD tyValue=REG_SZ; DWORD cbValue=100;
if(RegQueryValueEx(hReg,"ComputerName",0,&tyValue, (LPBYTE)lpValue,&cbValue)==ERROR_SUCCESS)
MessageBox(0,(char*)lpValue,"RegQueryValueEx",MB_O K);
}