Funny, I had a similar problem with my an35n.
Does your pc turn on at all when you hit the switch (i.e. the cpu fans and stuff start moving around inside), but doesn't actually boot? If this is the case, try clearing the CMOS via the jumpers, it should at least get your pc booted up again.
Also, would your pc turn on only if you resetted the switch on the back, and then tried it? If this is the case, then could your case possibly be old? The power switch cable connected to the mobo could be faulty (the wires could be loose or just plain bad). This sounds likely as you have tried two seperate power supply's, negating them as an outright possiblity...
"Hows 'bout them apples?"