Your info is a bit sketchy.... It may be a virus, it may be your HDD. A lot of times Windows start-up issues are caused by improper previous shutdown where configuration files were not saved properly.
On start-up, you should hear the machine beep at least twice. (beep codes vary from one bios to the next, and are a signal that memory and keyboard at least have been detected). Then you should see the splash screen.
During the splash screen you can hit the pause button to read the screen. By hitting Delete, or F2, or whatever is described on the splash screen you should be able to confirm that you can at least get into the Bios setup. Don't make any changes for now. The bios and the splash screen should both show you all the HDD's and other devices detected.
During the splash screen you can also hit the F8 key which is specific to Windows XP and will not be displayed. This will take you to the Windows boot menu. If you can get there, the first menu item I suggest you try is "Last known configuration that worked". (Hit F8 many times during splash screen).
If that fails, you can also try starting in "Safe Mode", or "Safe Mode with Networking".
There is also a method to manually replace the config files with backups on the HDD, but try the above first and see what happens.