Create a new system restore point then download and install the drivers for the MB from here start with the chipset drivers first and test, if the computer is stable and all features work (audio etc) leave as is.I never manually reinstalled drivers.
The Valley benchmark results, the fact that you have been able to run the program without it crashing suggests that your hardware is stable, the FPS suggests that you have a bottleneck and with you having an entry level dual core CPU that is the most likely culprit, the Game Debate review here also suggests this to be likely.
Odd that things were fine for around 5 months getting 100+ FPS at high settings, can I ask what games you were playing and getting such FPS.I have had this computer for about 5 months now, I custom built it. When I first got it, It could run games smoothly with 100+ frames at close to max settings,