you can do a system restore if any virus or system errors is infected your pc it will restore your pc in a previous state here are steps to restore the system
1. Click Start, point to All Programs, point to Accessories, point to System Tools, and then click System Restore.
2.On the Welcome to System Restore page, click to select the Restore my computer to an earlier time option, and then click Next.
3. On the Select a Restore Point page, click the most recent system restore point in the On this list, click a restore point list, and then click Next.
4. On the Confirm Restore Point Selection page, click Next. System Restore restores the previous Windows XP configuration, and then restarts the computer.
5. Log on to the computer as an administrator. Then, click OK on the System Restore Restoration Complete page.
If you successfully restored your computer to a previous state and the computer runs as expected, you are finished.