GPU Usage drops to 0%

[Laki89]

The DDR3-1333 hurts for sure, especially if it's a single stick.

Stock ram speed has nothing to do with system stability and fps drops
Only overclocked Ram memory modules can cause that

@Baner : I also recommend you to change psu to some reputable manufacturer: Chieftec, Cooler Master, Seasonic, etc. with at least 650 watt

Edit: Believe it or not but cleaning PSU and GPU with compressed air may solve problem for 2-3 months