Now I remember about comment on memory choices. Yes very picky with multi-CPU boards.
PSU is not rated by the MAX power. It is surge max power that PSU can provide for short time. For steady use, take a typical total watt and add 25% fudge factor and you have it.
For example you figured 300W, this is bit too low really. Ram, chipsets, video, network, etc cards can consume around 100-130W, dual CPUs around 200W at the most because of voltage regulator losses. Hard drives is typically 11-13W writing/seeking. If have another HD or two, That's 39W if have 3 hard drives for example.
Add this all up is nearly 370W, plus 25% fudge factor gives you
465W. A decent 500W PSU is sufficient.
Oh yea, fans are not power misers, many can eat up 3W to 5W per fan. High performance fans even eat up 10W and that's even for a 6800rpm 60mm whiners.
You don't have to buy stuff, borrow or test swap certain parts one at a time to isolate the problem. Quality ram is a MUST especially for multi-CPU system. OCZ, curical, etc are ones should have.