Over the past couple of months, my 2007 MacBook Pro (Intel Core 2 Duo) has been restarting unexpectedly. (Just as it sounds, the computer will shut off without warning, and then reboot normally. Sometimes, the computer won't even make it through the start-up process before shutting off and rebooting again.) The restarts have gotten more frequent over time; now, the computer can and will restart every few minutes. The restarts don't seem related to any particular application; they've occurred while surfing the Internet, typing in a Word document, watching a DVD, etc. I have noticed, however, that the problem seems to get worse the longer the computer is left on (perhaps as the computer becomes hotter?). The hardware test came back clear. I've tried multiple SMC and PRAM resets. I've also repaired disk permissions. Nothing has helped. Can anyone help me diagnose / correct this issue? I realize the computer is old, but I'd love to continue using the machine for Internet browsing / word processing if at all possible. Then again, I don't want to waste too much time on the machine if it's beyond repair. Thanks in advance for your input!