I used my old Seagate SATA HDD, optical drive and nVidia 8800 GT video card and installed Windows 7.
Everything went well but then it started randomly rebooting when idling or be being used lightly. It would be rock solid stable in game.
Thought it might be RAM voltage so up'ed it from 1.5 V to 1.64 V with no effect. Switched out the RAM for 6 GB (3 x 2 GB) Kingston DDR3 (1333) and had the same problem. Both RAM configs have been tried under fail safe mode with no effect.
Interestingly, I have tried installing XP and it reboots in the install phase (after getting through setup). This happens for both sets of RAM.
A quick scan of the "help wanteds" here would tell you YES, a dead, flaky, underpowered, or dying psu is frequently the cause of many problems.
There are 8-pins there for a reason, though mobos will often work with a 4-pin plug right up to the point that they won't. I gather that what's not said is your friend's slightly smaller psu had an 8-pin connector?
Maybe that's the fix, maybe it's not. But you have clearly proven your psu will not drive that mobo, so get a new one with the proper fittings.
"CPUs used to be powered by the 20 pin main power cable. Almost all current motherboards power their CPU with a 12 volt CPU power cable. There are two kinds: the 4 pin 12V cable and the 8 pin 12V cable. The 4 pin cable is often called a P4 cable (although it's a very bad name) and the 8 pin cable is called an EPS12V cable. You must plug a cable into this motherboard connector or the CPU will receive no power. The compatibility rules between 4 and 8 pin connectors have a lot in common with the rules for 20 and 24 pin connectors. The best choice is to plug a 4 pin cable into a 4 pin connector, an 8 pin cable into an 8 pin connector, or a 4+4 cable into either kind of connector. You can get adapters which will convert various kinds of power supply cables into both 4 pin and 8 pin 12V cables. You can plug a 4 pin 12V cable into an 8 pin motherboard and it will sometimes work properly but other times it won't work at all or will burn/melt the connector. As with plugging a 24 pin cable into a 20 pin motherboard connector, you can plug an 8 pin cable into a 4 pin connector and leave 4 pins hanging over the end but you can also have the same problems with things preventing it from fitting. It will work fine if it fits. If you're buying a new power supply then the safest choice for the long haul is to get one with a 4+4 power cable because it's compatible with both 4 and 8 pin connectors."