Black screen problem

[deflowvesper]

So recently i've been having this problem where my screen turns black all of a sudden and loses signal from my video card whenever i play a game for a certain amount of time. I tried cleaning my whole PC thinking it could just the fan not being able to do its job properly due to the dust, so i simply hoovered the dust off the fan and every parts of the motherboard. After putting back the PC together, i tested the game again and it seems it gotten worse, my screen goes black within a few minutes after launching the game. Im not sure if it is my power supply but i don't much have other unnecessary components anway, plus i've had this graphics card for almost 2 years now so i dont think its the PSU is the problem.

My current Video card is: Nvidia Geforce 9500 GT
Power supply: 300W
RAM: 4Gb

All drivers are updated. I haven't checked if the fan is spinning properly though.
Playing videos is fine, i only get this black screen when playing games. I could still hear the audio from a video playing despite having a black screen.

I ordered a new video card which will arrive tomorrow so hopefully this issue will be resolved, however it still concerns me what could be causing this. Anyone with experience has any theories?
New video card: AMD Radeon HD 6570
Its a cheap video card but its significantly better than the one i currently have.

 

[95Viper]

Is this a pre-built OEM system?

Did you check your temps on the cpu, gpu, and/or chipsets?
Yep, you need to check if the fans are working properly.
When you cleaned it... before putting it back together, did you replace the TIM (thermal paste)? That would be on the CPU and GPU.