Dead a7v266-c or what?

Hi,

I have a PC with an Asus a7v266-c motherboard. The system did not power on. Only the CPU and case fans were working. The HDD did not spin and no POST beeps or screen lights turned on. Today I unplugged the battery in an attempt to test the M/B and when I pressed the pwr on button nothing happened, no fans were spinning and I smelled smth from the M/b (the usual smell when an electronic system is burned) and the system is dead. However there is a green light on the m/b which is still on. Maybe the power supply unit is dead. Before this I had ordered a new CPU for this m/b (Athlon XP 2600+ AXDA2600DKV3C SOCKET 462). My question is how can I spot the exact problem? If the m/b is dead I have one new CPU left and I do not know what to do with it. To order a new m/b compatible with the new Athlon or to go away with a new PC? Also if I need a new m/b which is the best m/b compatible with the Athlon xp 2600?

......now the problem became very complicated.... I was instructed by ASUS support site to reverse the battery for 10 minutes and now the system powers on but only with the battery reversed. The HDD and CD-Rom drives work only without the IDE cable connected. When I connect the IDE cable the hard disk does not spin and the CD rom's do not eject the tray. There is no POST at all. no signal to the screen.

Thanks!