We had a virus. We believe Norton cleaned it. Now, it seems as though many Windows components are gone. The backup we did with Norton most recently won't work to restore. We don't have the original discs that came with computer -- we didn't know that we should have paid Best Buy extra to get them. I can't seem to find anything on the Microsoft site to help. I'm running Windows XP Media Center edition Version 2002 SP3
Download to your desktop, once download is complete double click to run. When prompted allow the registry merge.
I would also run Malwarebytes Anti-Malware (free) as a precautionary measure. Most AV programs will disinfect a system but leave remnants of the malware behind, making the PC prone to further attack. Malwarebytes is very good at cleaning up.