Intermittant Booting

[pansy309 at tds.net]

Greetings 

I recently installed FC5 on a dual boot system.  About 50% of the time when I boot it up, it goes cleanly through the boot process until it is ready to open the sign-in screen.  At that point the mouse pointer appears briefly, then the screen goes black.  About 30 sec later, a click can be heard from the monitor and the machine is locked up with a blank screen. Nothing short of pushing the power button will do anything.  When I do this, the hard drive will operate a bit and then it will shut down.  When I have to do this, the CMOS loads defaults.  I suppose that is caused by the unusual shutdown.  I have a Radeon 9000 video card and a Dell M781P monitor.  The other 50% of the time it boots up perfectly.  

Does anyone know why, and if so, how can I fix it?

DAR