New rig boot/reboot issues - HELP!

Hi all,

I've just built a new gaming rig, and I've been having a lot of problems with it. I've sorted most of the ones that aren't down to "Vista bugs and 64 bit system with 32 bit software" along the way, but one critical remains. I'm sure it's something simple I've overlooked, maybe a simple noob mistake... or rather I hope it is because otherwise it's HW failure oO

Basically when I boot it up, everything starts spinning - for 2-3 sec. Lights come on, case, cpu and gfx fans all spin up... and then it powers down completely. Now if I press multiple times on the power button with a specific timing it continues to boot after 4 rapid presses or so! It boots up fine, everything is running fine, I can play games, nothing is overheating, no issues AT ALL - untill the next time I have to shut down or reboot my PC. Reboot doesn't work, it just powers down fully.
This cannot be healthy! It must be an extreme strain on the HW every single time I attempt to to boot it and fail. I usually have to try 4-10 times to get it right.
-I've eliminated software as a cause for it not rebooting, because it even does it in BIOS. When I choose save and exit the PC should reboot, but it doesn't. It powers down.
-I tried swapping the power button to the reset button in case it was a dodgy connection in the button itself, but the same thing happens. I doubt it's that anyway since it doesn't explain why it wont reboot automatically.
-I tried disabling CPU fan warning at a certain speed (600rpm) in case it was shutting the PC down prematurely because of the fan being too slow to get into gear. No luck there.
-I've got the newest BIOS version.
-Just FYI all RAM tests I've run are passed.


Does anyone have any ideas? I'm getting really frustrated with this (not to mention scared that it's a component failing)


-----The rig-----
ANTEC NINE HUNDRED GAMERS CASE
ASUS P5NT-WS Motherboard
BFG 8800GTX 768MB Factory O/C
Intel Q6600 Quadcore CPU G0
Zalman CNPS7700-ALCU 120mm Super Flower Cooler
Corsair DDR2 TWINX 2GB PC6400 RAM (x2 = 4GB total)
Optiarc AD7173S x18 BLACK SATA DVD
2x400GB HDD WD SATA2 WD4000AAKS
Zalman ZM600W-HP ATX SILENT PSU
Windows Vista Home Premium 64 Bit
------------------

Hi g-paw. Cleaning the CPU/Fan will not help. When I put the rig together 2 weeks ago everything was brand spanking new and I applied my own arctic silver thermal paste (as good as it gets). Also as I said there's absolutely no issues with the machine under loads. Stability is perfect and heat is well within parameters.
I have checked with both Asus own Probe II and the hardware monitor in BIOS. Heating is never the issue. Besides this happens even on a fresh boot when the PC has been off all night.

The PSU is my fear as well though. I have a feeling it might be it. It should be well within requirements so it may just be faulty
I'll consider getting another one to test. It's a shame though, the Zalman PSU I have is very quiet, runs cool - and looks cool too.

Anyone else have any other ideas before I invest in a new PSU?