Could you please post the specs of your PC/Laptop? It currently sounds like your GPU (graphics card) is stuggling and may either be too low in power, or possibly too old or maybe failing. Without more info it would be very difficult to guess correctly.
I suggest posting:
The CPU model
GPU model and estimated age
Operating system (also whether it's 32 or 64 bit)
and the games that are having problems
This would be extremely helpful in diagnosing the problem. If you don't know how to get this info, please don't be afraid to ask.