I have a MacBook Pro (15-inch, Early 2008) that's currently running 10.7.3. I've been finding that it will intermittently freeze and then I have to shut down and restart the computer, but sometimes that will not fix the problem.
If I plug in an external mouse and keyboard, then I can move the cursor and type again, but as soon as I remove them, the problem persists.
I've tried resetting the P-RAM, reinstalling Lion, installing a new HD, and I've had the graphics chip tested and it's performing properly. If you have any suggestions on how to fix or diagnose, that would be very helpful. Thank you.