Extremely Slow PC

About a week ago I downloaded Intel's 'Progress Thru Processors' program to somehow transfer spare unused processor power when my PC is idol to other institutions to help them save the world, or some other crap like that.

Anyway, it came with a screensaver showing me climate change, and since for about 2 years my screensaver had been the basic Windows XP screensaver, I left it.

But about 2 days ago when I turned the PC on, I noticed after I clicked to login, the 'Logging On...' screen was taking ages to continue to desktop, until after about 3 or 4 minutes it finally did, but with no explorer running, until a few minutes later, and it popped up.

If I moved the mouse over icons and they were highlighted, it would strain the PC and take a little while for them to highlight, so I checked processes on task manager hoping to find some unknown program hogging all my processor power and I found a process called Boinc********** (*** was the text and numbers that followed it after, which now I don't remember), and it was using in excess of 54,000k of my memory, (I have 1GB RAM) so I chose to end the process, but it did not end and continued, so I came to the family PC downstairs to do a bit of research but couldn't really find anyone with the very same issue (as usual) .

Anyway, I wasn't having very much luck, and since my parents had been away and I had the lovely big TV downstairs and this PC, I hadn't bothered much with sorting it out, but they're back now, so I guess it's time. Normally I don't try a system restore, I always try to sort out the problem there and then instead of reverting back to a previous date for the PC, but I decied to try it anyway.

It must have taken my in excess of 3 hours to actually get the system restore application running and set, and my computer proceeded to restore, but when it came to 'Shutting Down...', this screen stayed on my PC for at least 4 hours, until I thought it had just crashed. So I manually shut down and restarted the PC, only to find that when I log on now my PC goes even slower, explorer never begins to run, and I am greeted (very slowly) by the 'System Restore was interrupted' notification, and the application begins to run again, only this time when i try to reset the system restore, my computer reaches a state in which not even the mouse moves, even though when I press tab I can still see the buttons highlight and change, but when I press enter, nothing happens.

So! Any help would be greatly appreciated. Since I have no idea where to even start! And safe mode does the same thing.

Thanks!

 

Just to add a bit more, i'm running on a 4 year old (I think) PC, still performs well for what I use it for, listening to music and browsing online, I tend to use my Xbox for gaming nowadays, so I've never needed to upgrade to a better PC because I still get good performance from this one, a part from a few problems I tend to run into along the way.

Windows XP Pro SP3 is the OS, and the processor is an AMD Athlon 64 4200+ I think, I've honestly not checked in a long while, and the graphics card is an ATI Radeon X800 GTO 256mb, if that information is any more of a help.