I have a Benq Joybook 5000 which is coming up for 6 years old now. It will boot fine but after between 1 and 5 minutes after boot the keyboard will stop functioning along with the mouse pad and all other buttons. The only way to switch it off once this has happened is to hold down the power button.
Once i've done this then the laptop will refuse to boot, the BIOS doesn't even start up but the lights and fan come on. If the laptop is left for an hour or so then it will again boot but the keyboard issue returns as above.
After trying out a few of the suggestions below it would seem that the problem is hardware related. I've done a memory test using Memtest which passed OK. I've now booted from a Linux live cd, then opened up a word processor to leave the cursor flashing in an empty document. After 5 minutes the keyboard and mousepad etc stopped working again, same problem as in Windows but the computer itself has not crashed or locked up, the cursor is still flashing in the document. The computer seems fine in all other respects apart from the fact that the keyboard and mousepad stop working.
I've also plugged in a USB mouse after the keyboard and mousepad have stopped functioning and it worked fine.
Any suggestions further to this would be welcomed.