Strange problem with PS/2 mouse & keyboard

Hey there everyone, I would like to share with you my problem so that we may find a solution or find out what is wrong, so here is my problem:-

When I open my computer and log into windows, everything goes fine but after some time or when I open a game or so, my mouse and keyboard stops working AND ONLY my mouse and keyboard then I have to restart my computer so that they work again, everything else works fine and my proof is that when I play an online game for example, everything is moving as nothing wrong going on.
But well there is more to come,
When i shutdown my computer and exactly when it tells me "Windows is shutting down" the mouse and the keyboard works again, the mouse can move and the keyboard respond on clicking the locks also if I unplugged the mouse or keyboard and plugged them again, the keyboard's 3 locks check lights up and the mouse produces its light but they don't work.
I tried to reinstall windows but the problem persists even with Windows Vista I had the same problem and I also tried safe mode on both and still I have the problem.

I have a Pentium 4 processor with 3.20 GHz and 768 ram memory

Hamadamoh