I will give you the step by step guide to system restore but before that let me tell you a system restore will only uninstall applications and software that you have installed in between the today and teh date that you are restoring it to, but will NOT SOLVE YOUR PROBLEM
To use System Restore to restore Windows XP to a previous state, follow these steps:
1. Log on to Windows as Administrator.
2. Click Start, point to All Programs, point to Accessories, point to System Tools, and then click System Restore. System Restore starts.
3. On the Welcome to System Restore page, click Restore my computer to an earlier time (if it is not already selected), and then click Next.
4. 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.
Note A System Restore message may appear that lists configuration changes that System Restore will make. Click OK.
5. On the Confirm Restore Point Selection page, click Next. System Restore restores the previous Windows XP configuration, and then restarts the computer.
6. Log on to the computer as Administrator. The System Restore Restoration Complete page is displayed.
7. Click OK.