A7N8X not posting after some restarting issues

I had been having some restarting issues. When in windows xp, I would go to shut down, the unit would shut down but then start up again. I would have to turn the psu off to shut down the unit. When turning on the unit I would flip the psu switch back on, and press the power button, the unit would turn on for about 3 - 5 seconds and then shut back down. When I did get the unit to stay on, I would have to reset cpu settings in the bios. In the end now the unit is no longer posting. I hit the power button, the leds turn on, but the motherboard doesn't post. I went ahead and replaced the psu with a new one. My next thoughts are to replace the bios battery and possibly replace the bios chip. I really can't complain the unit has worked well for about 5 years. Just wondering if anyone else has any thoughts. Thanks

+1. Also check the power switch and wires for shorting, but this sounds more serious.
If it has been five years, then by all means replace the BIOS battery. It is almost certainly dead. Not sure it would cause this symptom though.