Probably an OS X problem and not a hardware problem, so I am posting this here.
12" Powerbook. When starting the machine, it got stuck; happened just once. The grey screen with the apple showed up, but the rotating thingy below the apple stopped rotating for about 30 seconds. Pressing and releasing the power button resulted in a normal restart. Nothing unusual in the system.log for the failed start. Not sure how to check the system diagnostings for the failed start, but it shows that it passed the diagnostics for the next successful boot.
Any ideas what may have gone wrong?