mouse and keyboard frozen

I was just chatting and surfing the web when all of a sudden the mouse wasn't moving, totally frozen, couldn't move at all, so I connected my external mouse and that one worked, but when I tried to google the reason for this random mouse freeze I noticed that the keyboard wasn't responding either.

Rebooted and now everything is working fine. Searched here for a similar problem and found only one or the other.

I have an early 2008 MBP, no problems with it whatsoever, except a replaced battery about a month or so ago.

Any ideas? suggestions?

 

it happened again a few hours ago. Almost a week after the first problem.
I was using parallels and all of a sudden I couldn't move the mouse, same for the keyboard.

An external mouse however worked so I rebooted. Again all working perfectly fine.

What should I be looking for? Is there a log file or a diagnosis I can run?