System won't boot

[sadVistaUser11]

I have a 32 bit Vista machine which won't boot. The original problem is that there was a virus on it. A friend ran an antivirus program which removed the virus, but also deleted some windows system files which made it not startup. When I turn it on, the Windows logo starts to load, then the screen goes black, it plays the startup sound and then nothing.

Initially, I was able to go into Safe Mode. I checked the Event Log and there was nothing suspicious or helpful. I did a full virus scan with two different antiviruses (McAfee and AVG). I ran the sfc /scannow utility and it failed saying that it could not repair the damage. I also ran the Startup Repair utility and it found no problems.

A friend suggested that I should uninstall the latest service pack and then re-install it in the hopes that it would repair the damaged files. However, after I went to uninstall the service pack, it restarted, and now I can't get into safe mode anymore. Safe mode stops with a message "Service Pack did not install. Reverting changes". However, it never finishes reverting changes and sits in an infinite loop.

Does anyone have any ideas? Thanks!

I also should note that I tried System Restore and it could not find any restore points. I believe the virus wiped System Restore before the antivirus program removed the virus.