Try one of these: http://www.techmixer.com/free-bootable-antivirus-rescue-cds-download-list/
Make the CD on a different machine and then boot to the CD on the suspect computer and let it run. If you need data from the drive (assuming no backup was made) then also try this:
Disregard the Vista mentioned in the page, as it will work with any Windows OS. You could also give EasyBCD a try: http://download.cnet.com/EasyBCD/3000-2094_4-10556865.html
If there is a virus after all this, then wipe the drive with DBan : http://download.cnet.com/Darik-s-Boot-and-Nuke-for-CD-and-DVD/3000-2094_4-10151762.html and reinstall Windows 7.
My laptop is not booting normally ever since I downloaded a file knowing that it might had a virus.....when i try to hit f8 at start, all i see is a black screen and when i changed my boot sequence to DVD, and inserted windows 7 or windows vista's DVD, i get the message: press any key to boot from CD or DVD: Error could not find bootmgr. If I try to boot my laptop with windows xp cd, i get the message: memory over flow error. and If i try to boot from the vista recovery DVD, the windows hangs upon: Setup is inspecting your computer's hardware configuration.....
My laptop came with vista but i upgraded it to windows7 when it came out in the market. Thats the reason i made those recovery DVD's before formating vista just in case if i needed my computer in the state that it originally came in .
It is a Acer Aspire 5630 laptop with 2GB of RAM and 320 GB of hard disk space.