no reboot if left sitting after shutting down

[Tepin]

I'm running an AMD 1GHZ @ 1.2GHz on a Abit KT7 MB. If I tell it to shutdown it does, but if I leave it sit without physically powering it off totally via the power bar it will often not power back on (it sounds like it's coming up, but there's no video post) The only solution is to pwr fully off, clear CMOS and power back up (and reset all the darn CMOS setting so what I had them at)

Anyone else experienced this - or better yet does anyone have a fix for it?