PC Freezing In Certain Games And Programs

Hello everybody
Ive been having this problem that my Pc is freezing without a bluescreen or reboot, it just plays a loud buzzing noise through the speakers and the Pc is completely frozen, I have to manually shutdown via power button. This only happens while playing playing Bioshock 1 for about 10 mins, Shogun 2 once every couple of days. Fl studio is the only program that did freeze my pc but i found out using the Fl Studio extended memory.exe fixed the freezing. this leads me to believe that i have failing ram but wouldnt it have the same effect on other games I have such as CSS, Arma 2 Dayz, Saints Row 3, Race 07, GTA IV. all these games i run at highest settings possible for my system. The thing is I checked the ram via memtest about 3 months ago and found 1 bad stick and had to remove but the rest shown no errors.

System Specs

AMD Phenom ii X4 960 i believe.
Asus Nvidia Geforce GTX 560 ti cue2 1gb vram model.
3 sticks of 2gb kingston ram dont know which model sorry.
Any more info needed ill get off my ass and get it.
Is there any other known causes for this happening or is it just ram?
Any help will be greatly appreciated