^ Good way to get hacked there.
Give the Gnutella people your IP and then all your system specs - genius...
You also didn't build that - it sounds EXACTLY like a setup for some of the older HP Pavillion models... Freud.

Anyway - All these guys gave you was air! I'll make it simple.
You can fix your problem(s) rather quickly:

1) Install / Run any anti virus software you already have.
Uninstall each one as it fails to pick anything up.
Lastly, get what I use: Kaspersky Internet Security - It's great. Some of the other links to software can be mal-ware, being FAKE anti-virus programs!

2) Defragment your system - get unused sectors "recycled" for reuse.

3) If any particular program causes your system to slow, unintall and reinstall it - that could be what's messing up your system or "holding" a virus. After reinstall, if you STILL get issues with the same program, try tweaking settings.

4) When using any online resource, make sure you have PING usage blocked somehow, be it with a network router or firewall.

5) If you STILL have issues, it may just be time to get some more memory (and Hard Discs are about $70 or so for a good 120 Gigabytes) or some more RAM installed.

All of this depends on the time and effort or funds you're willing/wanting to use of course.

On a sidenote - it's nice to see somebody else who liked Final Fantasy Tactics.
I used to hack the crud outta that with GameShark! <(^.^)>
Be sure to try FF7 - if you can get hold on it somehow (GameStop/eBay) - it's arguably the BEST ever.
I guess they're remaking it - at least, there's a demo going around for a remake for PS3 & MAYBE Xbox360.