You should state the version of Windows because the methods of dealing with virus/trojans varies between them.
If you are using Windows 98 /98 SE, try running the scanreg /restore command in DOS mode to backdate the system files to a date prior to the infection.
For both Win 98 and XP, use the TweakUI Repair features to recover any system functions that might have been taken over.
SCANREG
Start up and press the F8 or Control key to bring up the boot menu. Select to boot into the DOS command line. Enter scanreg /restore. You will be presented with several CAB files that contain backups of the Windows Registry and other critical system files. Restore one that predates the problem and that should allow Windows to boot properly.
Since the restored CAB file (one of a default of five CAB files in the C:\Windows\SYSBCKUP folder) contains the system files - user.dat, system.dat, win.ini, and system.ini - was created on a pariculr date, any changes that were made to the system after that date will have to be repeated.
You will obviously not repeat any change that you suspect caused the problem in the first place unless you want to make sure that it was indeed the cause of that problem.
To fix the Registry use scanreg /fix - and to optimise the Registry use scanreg /opt.
If scanreg /fix gets stuck half way through just reboot and, if necessary, use scanreg /restore to recover the situation. But most of the time the system will start-up after a Ctrl+Alt+Del restart even if the scanreg /fix utility gets stuck.
Obtain all of the TweakUI info you need here. - PC Forrest (Plenty of PC information - MS DOS, the BIOS, Windows, swap files, TweaK-UI, Registry hacks, etc.)
http://www.forrestandassociates.co.uk/pcforrest/tweakui.html
Eric,
http://www.legge40.freeserve.co.uk/BuyerBeware.htm