If anyone else needs a temporary solution I think it may work for them if there’s a serious problem with ubuntu linux.I set up ubuntu 10.04 on an IBM thinkcenter A50…(OK, that’s what I was given so I made the best of it).Anyway, I would come back to the lab every morning and find the computer in something like sleep but it would not wake up at all. As I had installed a raid array and had a share this was not good….it was a serious problem.I disabled everything in the bios, disabled acpi in the kernel options, disabled sleep in the power options within Ubuntu to no avail after losing a few days troubleshooting.
I even tried poking the monitor off and on and various such options.At that point the following options were available that I knew of:
1) Install another linux distro (e.g. ubuntu server)
2) Install another OS e.g. Free NAS
3) if 1 and 2 failed build another pc using another motherboard.
4) Try updating the kernel…

However, being in a jam due to time pressure for other tasks I decided to try adding a cron script to write to a file every few minutes. Surprisingly the server is still up after 2 days and has stopped sleeping.

I suspect reading from a file every 20 minutes, or writing to dev/null may also stop the idle state.

Just my 2 cents about this very frustrating problem and a dirty hack which worked.
“Taking any old pc and calling it a server doesn’t make it so” .

Menelaos