Regular BSOD since graphics card fan died, OS vers. 6.1.7600.2.0.0.256

Hello I'm looking for help in figuring this problem with frequent BSOD crashes. It started after the fan broke on my graphics card and replaced with with a friend's Gefore 8800 ultra(i think). I figured it just took too much power (500earth watts psu). However, replacing the fan on my HD 4870 512mb I changed it back. The fan now connects to the motherboard, in case that's important. I found it would crash MORE frequently when playing games as well as having stuff on in the background (windows media player + league of legends certain death). Anyway, after visiting this site I wondered if the drivers had been messed up when I changed ATI for nvidia or maybe I had faulty memory. In the end I took one stick out and wiped my computer. I was safe for a week maybe, before a BSOD. Then free for a few more days, and more and more it's happening more regularly.

So I've come to you guys to hope you can make sense out of this. The graphics card hasn't seemed to be broken at all in any way other than the fan stopping. I was about to buy a new one but realised it didn't seem likely to be the cause and that basically only the processor is in the clear. Details following and diagnostic tool data attached. Thanks for reading and for any help.

Problem signature:
Problem Event Name: BlueScreen
OS Version: 6.1.7600.2.0.0.256.1
Locale ID: 2057
Additional information about the problem:
BCCode: 124
BCP1: 00000000
BCP2: 85B3101C
BCP3: B62A4000
BCP4: 00000145
OS Version: 6_1_7600
Service Pack: 0_0
Product: 256_1