[X-Newbies] Sleep mode

[Robert Green]

I have an intel mac running 10.4.11. When I set the sleep mode to  
automatically put the computer to sleep after a set time it won't  
wake up. I can hear the computer running but the screen stays black  
and I have to restart to get it working again.  Screen saver is set  
to off. If I set sleep to never but use the power button to put it to  
sleep it all works well.  The sleep mode has been working fine until  
recently and I checked the settings which are the same as they have  
always been. I did all the routine maintenance  suggested by Randy  
Singer on his webpage - http://www.macattorney.com/ts.html - but that  
didn't help. Any suggestions?
Thanks
  Rob