Faulty Asus A7V133 ?

Hi there,

I've just bought a new mobo Asus A7V133 with an Athlon 1G.
When I first mounted them in my tower, I pushed the button, and the thing started to run fine...until I had to switch off.
After that, the behaviour of the PC became quite erratic ! In fact, the pb is simple to describe : when I push the power button, sometimes the PC would turn on, sometimes not !! And most often, it doesn't.
I checked every connection, all is correct. Then, I unmounted all parts on the mobo and remount them one by one. The pb even happened when the mobo was only connected to the ATX power supply !!
I don't think it's my PS (300W), as it works perfectly with my ancient (!!) Asus P3BF.

Of course, I brought the whole thing back to my retailer, but he couldn't reproduce the thing, though I don't think he worked enough on it (10minutes is a max !)

Do u think the mobo could be faulty ?
Thanks for ur helps

zentrad