Keyboard And Mouse Problems

I inserted a memory stick to a USB and it worked fine. Second time my PC locked up. After re-booting I discovered that the mouse and keyboard weren't working. I attached 'same' from another computer and they worked fine. However, after a while it still locks up and my mouse only works if I unplug my keyboard and plug it back in. ( Unplugging the mouse makes no difference) I reckon something has happened after inserting the memory stick?
Can anyone advise me how I correct this problem permanantly? I have another computer alongside and can transfer files and things.
Thanks Herby