Startup & Restart Problems on Athlon XP3000+/Abit KD7-G/WinXP

Hi - I am having startup/restart problems with my PC. Sometimes (1 in
10?) the PC does not start when I power on...it just hangs on a black
screen and I have to power down and up again to get it to work. Also,
it will not restart when I choose "Restart" from within WinXP.

My system is:

AMD Athlon XP3000+
Abit KD7-G
Hercules 3D Prophet 9700PRO
Corsair TWINX1024-3200LL DDR-DIMM
2 x Western Digital Caviar 120GB IDE 7200RPM
NEC CD-brenner IDE 48x/24x/48x
NEC DVD-brenner IDE ND-1300
WinXP Pro

I am using the latest BIOS for the motherboard and I am using the
onboard network controller.

Any idea what could be causing these problems?

Thanks.