The only thing you could really do is play around with teh settings, like in the bios the different sleep states and what not to see if it helps. If not you could try updating the BIOS (even if you have the latest you can still reflash it) otherwise, its a matter of reinstalling the OS im afraid.
Hope this helps.
I was finally able to figure this one out after searching for qite a while. I had an old hard that I added to my tower months ago and the hard drive didn't support remote sleep power saving features. Eveything else would attempt to come back up this drive causing me to think sleep had failed.
Good you got it fixed