I had an old e-Machines PC (T5234) laying around, and I wanted to make it into a HTPC. It booted fine in the stock case. I took the mobo, power supply, cpu and hard drive and put it into the new htpc case I bought. Now, half the time I go to boot up, it starts loading XBMC off the hard drive, then powers off completely. Sometimes it'll fully boot into XBMC and then it's fine. I can sit in the BIOS forever as well. I bought a new PSU, and it's not that. The only different thing I added was an 8400gs card (doesn't require external power)...but I've also removed that thinking that it was a power issue, and it's not - it'll randomly shut off during boot again.