I recently swapped out the hard drive and RAM in my wife's Late 2008 Macbook for an SSD and 8GB of RAM and it worked fine for a couple of days. Then, sometimes it would shut itself down. This started becoming more frequent until the laptop would shut itself down a minute or two after booting (this is with Mountain Lion). I put the original hard drive and RAM back in (running Snow Leopard), and the same thing happens. I tried booting off of the old Windows partition on the old hard drive, also shuts down. The weird thing is that sometimes before shutting down, in OSX it would ask if you were sure you wanted to shut down, like the power button had been pushed. I thought maybe it was a problem with the power button, but if you leave the Macbook at the boot menu (holding down Option), it will stay on indefinitely. I'm really at a loss for what happened, aside from me botching something in the replacement. One other thing of note, when I went the replace the parts, the battery was bulging to the point where the lid was jutting out on the bottom. I removed the battery, but possibly the bulging broke something as well.