My computer refuses to sleep (even on command)

[fairnymph]

I've had this problem for about a month when I was in Tiger. I just installed Leopard, and I'm still having the same problem.

The hard disks in my Mac Pro will not go to sleep, not after the 15 min I have them set to go to sleep after in sys pref, and not when I directly command from the apple menu.

This is EXTREMELY ANNOYING and really driving up my electricity bill. Please help!

 

[fairnymph]

So, I've tried multiple sleep commands in a row. Once on the 3rd try this successfully put the computer in sleep mode. Twice it's caused my computer to crash.

HELP!