Need more information. What games are you trying to play? Have you checked out the temperatures of your CPU/GPU? Have you tried to reset your OS to factory settings?
Do you still have a warranty? If so, you're going to want to figure out which part is causing the issue. Do you have slow loading times? Could very well be the HDD. Do you have trouble with multitasking? The issue might be the RAM.
Can you disconnect your GPU and try to run a few games on integrated graphics? Switch back to the GPU on the same games. If the CPU can run them somewhat fine, or as good as the GPU can, then the GPU is the issue. If not, it might very well be the CPU.
It could also be the power supply you're using. You didn't mention anything about one.