I cannot start the computer

I cannot start the computer by a virus that I could not remove, turn on the computer tries to start until I get:
program not found - skipping autocheck
also tried to run safely and nothing
thanks

1. inserted the CD Win XP SP2, and BOOT as if you were to install XP.
2. It will ask you if you want to repair or install. Select Install
3. Then again ask if you want to repair or a new installation, select repair.
4. Start copying files, follows the installation process.
5. your information is not erased remains intact.
6. End of repairing, restart the computer

If the virus that nod32 had detected, I sent it to quarantine, I have installed servic pack3, which restarted 2-3 times.