I am a bit perplexed. I have an S3. It reboots during the silly welcome video after boot. Caps are not bulging, and I even changed the power supply for a new (pull) one that I bought off of ebay which also does not have bulging caps.
I changed the hard drive from a WD green to a Seagate a few weeks back using an image I saved off of the original drive years back just in case the drive was the problem. That worked for a few weeks, now it is back to where it was. Kickstart 54 passes and kickstart 57 runs for about 15 minutes after the GSOD then reboots and brings me back to where I started.
If it matters, the fan was replaced about a year back and it is spinning just fine.