Ever since I reinstalled Windows 7 Pro, I'm having issues with sleep mode. It happens on average once per three times I put it to sleep, where my machine won't wake up again.

I Googled that this might be related to hybrid sleep mode, so I disabled that. I also looked through event viewer and the issue appears to occur when actually putting it to sleep, and not waking it up:
>The previous system shutdown at xxx on yyy was unexpected.

When I wake it up, it seems to go through all or most of the motions - as in, I hear my hard drives and fans spinning up - but the screen stays black and I have to use the power button to shut it down and turn it back on.