F8 hangs after 10 minutes inactivity on Dell optiplex 755

[Mickey Bankhead]

I have some new dell optiplex 755 desktops.  F8 installed great, but 
after 10 minutes of inactivity, the machine appears to be locked up / 
frozen. The mouse arrow pointer will still move around, but mouse clicks 
don't do anything, and the keyboard won't respond. 

CTRL-ALT-BKSPC will crash X back to a black screen, but that's IT.
CTRL-ALT-F1 will get me a log-in prompt, I can log in, but the init3 
command will hang after 10 seconds or so

I suspect it's the power management trying to go to sleep or shut 
something down, but I've got limited options in power management, and 
with everything there set to NEVER, it still happens.

I can use the machine for an hour if I don't let it get idle...
PS. Related? - the Screen Saver screen will NEVER come up - I just get a 
blank white window where it should show the screen saver options, but no 
items on the screen...

Thanks in advance!