Windows Update destroyed my PC

So I installed a critical Windows Update and now what I formerly used as my gaming PC acts as if it was built in 2005. Specifically, everything has dratically slowed down: it takes about 2 minutes to boot, my Windows Index rating dropped from 6.2 to 3.3, and worst of all, games which I've run on highest settings up to 121 fps have dropped to 23 fps. I've tried a system restore, making sure my drivers were up date, a full system malware scan, and even freed up 25 GB on my hard drive, so does anyone have any idea what to do?

Specs: Quad Core Intel Core i7-37020 2.6 GHz
8.00 GB RAM
Nvidia NVS 5200 Graphics Card
Windows 7 64-bit