I'm not sure if this problem is a hardware or software problem, here it goes:
I'll start with the DVD drive. When I boot up the G5 the DVD player ejects just fine but after the computer has been on for a while (i tested today at about 45 mins. to an hour) I can no longer eject the DVD drive.
I moved the DVD drive to the bottom slot because the outside door is sticky and that did not help.
The same thing happens when I use toast. When the computer is freshly booted it will open up without error. After the computer has been on for a while (45min. to an hour) I can not open toast.
Are these 2 things related?
I tried turning off sleep in the preferences also.
I'm not sure if you have a G5 or an Intel Mac Pro. The Chip is irrelevant here, but these are two different processors in the same shell.
It sounds like your system is having difficulty with the DVD drive; it's hard to say if this is because of overheating, or some other factor. The drive no longer ejects and software (you don't mention the version) that talks to the drive refuses to launch.
Next time it stops working, I'd like you to go to your utilities folder, and open up system profiler. This application has a list of everything connected to your computer–including whether or not a CD/DVD drive is available. My instinct, is that when both of these issues show up, your Macintosh no longer believes it has a DVD drive.
Why this is a problem, is difficult to say without seeing the actual machine–it could be heat related problem, a problem with the drive, a problem logic board, etc. but a very least this is the right step for a good diagnosis.