Problem with keyboard becoming intermittent

Recently my wife's HP G62 laptop running Home Pro 7 has started having am intermittent keyboard. At first I thought it was the wireless USB keyboard/mouse she had plugged into the machine, but the same happens with just the built in keyboard (the mouse seems to function fine). The problem is that randomly the keyboard will stop working in applications and won't work again until a reboot. The keyboard seems to work fine in safe mode and actually works fine for typing in things like the run box in the start menu, but it will cause firefox and microsoft office to hang. I cannot seem to find what is triggering this condition (coming out of sleep mode, etc.), but it sometimes can be fast, other times it can take a day until it happens again.

Has anyone else seen this? I am perplexed because the mouse functions fine throughout all of this and the keyboard is obviously fine since when the symptoms occur, I can type in the run box fine.

That is a great idea, thanks. a couple of days in and still no keyboard issues, so I am about to start adding in apps to see who the culprit is. thanks again!