My Computer is being Retarded!!!!!?

I think there is a trojan in my computer. I tried fixing it through safe mode, antivirus, internet scans..... but nothing has worked so far. I just want to delete and reinstall everything on my computer to it's out of the box/factory state. I don't have a backup disk. (yes I have tried System Recovery and that is screwed up too). I have a dell Dimension E310. Is there any backup CD's I can buy? Or some Free (don't have to register or have some product key to do everything) that can reinstall everything? Please Help Me I Have Been At it for 10hrs. I think I have probably done more damage than repair!?

My Computer is being Retarded!!!!!?best antivirus software

You can create your own XP setup CD.

My Computer is being Retarded!!!!!?firewall

First step....backup/copy ANY files you don't want to lose....Burn it to a CD or DVD, or external or flash drive if you have one...

2nd step...Reboot, and start pressing the F10 (I believe) key...This should take you to the System Recovery program, and from there it's fairly simple...Just remember that ALL of your files will be DELETED (music, pics, documents... EVERYTHING).

If hitting the F10 doesn't get you there, you will have to call Dell for the sequence to start the System Recovery...(F10 works on HP/Compaq systems for sure)