Enormous Lag!

Hello.
I have a PC which has nVidia GeForce GTX 560 Ti by ASUS. It is about 1 year old.
I've had graphics card driver update problems as far as I can remember (the PC is self-built).
So, yesterday I tried to update my drivers for the 100th time and I removed the nVidia drivers from Control Panel, while I ran a virus scan with VIPRE and it found 3 viruses and removed them, then I rebooted my PC and tadaa! The computer lags at desktop huuugely and I can't do almost anything. When I do. Ctrl+alt+del it gives me an error in about 30 seconds complaining about some security and that If the OS is not responding I can use ESC to shut down or use the power button.
So now I'm just sitting here on my phone with my laptop just sent to asus care center wondering why bad things happen to good people.
Any help is appreciated, thank you.
EDIT: my OS is windows 7 ultimate 64bit.

UPDATE!
Okay, now I can actually use my PC with 800x600 graphics, but cannot install the graphics card drivers :S
Any help?

Okay, I had a problem with my laptop so I cannot use it, sent it to ASUS 2 days earlier.
Now my PC has this problem.
Here are the parts in the computer:
Intel Core i5 2500K 3.3GHz
MSI P67A-G45 DDR3 CrossFireX
Kingston HyperX Genesis 2x4GB DDR3 1600 MHz
Cougar CM 550W modularic ATX-powersource
Samsung 1TB SpinPoint F3 3.5" SATAII 32MB GDDR5 2xD
Noctua Processorcooler NH-C12P SE14
There may be more but those are in my shopping list of what I bought :P

Oh and I'm downloading win7 ultimate x64 iso file to see if reinstalling Windows helps.

Glad to help. With Windows sometimes the easiest solution is to just reinstall. Just make sure you keep backups!

I did :)