I have a very similar problem!

I have a MSI Neo2 Platinum, and an Antec TruePower 550w.

The PC was fine for about 2 days, then the next time I went to turn it on... the Mach II GT turned on but the PC wouldnt start.

Then I switched off the PSU and turned it back on again. The PC's fans started up for about 1 second and then stopped again. The power button on the front of the PC seems to do nothing. Yet everytime I switch the PSU on/off the PC fires up for a second!!

Assuming that the PSU had blown, I hooked up my Antec TruePower 430w and got the exact same thing!!

I then changed the CPU from an FX53 to a 3500+ Winnie.. same result. Changed the RAM ... same result. Changed the gfx from a 6800 Ultra to an Ati 8500..same prob. Took the mobo out of the case (as i thought it could be shorting on the mobo tray... same problem!!

I RMA'd my Neo2 and the new one worked fine for about 2 days, then all the same problems started again.

I have now returned this board aswell and have opted for the Asus A8V Deluxe, although Ive heard this mobo is not as good a clocker as the MSI, I would much rather have something with a little bit of stability!

REALLY FED UP WITH THIS MSI BOARD!!

Ps.... some of the people over at www.overclockers.co.uk are reporting the same problems, weird if you ask me!

* PPS... now that Im going from a nforce3 chipset to the Asus (via) chipset, do I need to uninstall the old mobo drivers and reinstall all the new ones, or do I need a full reformat??

Thanx a million guys!!