GET RID OF NORTON...They SUCK and are a memory / proccessor HOG!
My preference is trend micro's internet security suite, can get off ebay for cheap! We have used Trend all my past companies, one of them being Intel. 8^)
Try reading over this site
http://www.ubcd4win.com/ or
http://www.ultimatebootcd.com/ and do some virus/spyware scans on your current installation.
A good WinBlowz box with a good admin will run for a while. I have an XP box that I built about 4+ years ago and still running the same install, and has been running as my main pc for email, FTP Server, MP3 and DVD storage and is on 24/7 without any OS problems. I just don't take any MS updates. However I also don't surf the web and play around on that box....that what my laptop is for.
As for Linux, granted the new Distro's are very user friendly to install but hard to get some things to work on them, such as CD recorders, etc. But all the software is free.
Mac's lets not get started on that...
As a last resort, you could go buy a new Hard Drive from Best Buy ,etc. Install it in the PC, install a new OS, install a virus protector then hook up your old drive as a slave drive (see jumpers) and copy the data you need and wipe it when you are done.
~K