Computer turns on but doesn't "regain consciousness" after sleep

I've been having continuing problems with my computer waking up from sleep, and I'm wondering if anyone here recognizes the symptoms and knows what might be causing it.

When I manually put the computer to sleep and then wake it up ten seconds later, it wakes up just fine, but when the computer goes to sleep on its own and has been asleep for half a day, when I shake the mouse, the computer powers-on, initializes its optical drives, and the SDD/HDD light shows activity, but the screen never switches on. The SDD light will continue to flicker randomly as if there is real activity going on, but even after several minutes, the screen does not come on.

One thing that occurred to me is that it could be a video-only problem, and that the computer is actually "awake" but simply not sending signal (or syncing) to the monitor. To test this, I tried enabling system sounds -- the logon/logoff and USB connect/disconnect ones in particular, with the idea that I would listen to see if it made sound when waking up or when connecting/disconnecting my phone from the USB dock -- but it didn't make any sound when waking up after a long automatic sleep.

I also tried disabling PCI Express power saving and USB suspend, but this did not help.

Any ideas?

Welcome to the Forum.

Please edit your profile with ALL your hardware specs. System Info - See Your System Specs - Windows 7 Help Forums

Did you checked the Control Panel\All Control Panel Items\Power Options\Edit Plan Settings - Change advanced settings?
There should be a control for your graphics card

OK, I've updated my profile with all my specs.

I've tried fiddling with my Power Options advanced (administrator) settings quite a bit. There's no "graphics card" controls there, but there are controls for the monitor, and I've fiddled with those several times.

One thing I discovered today was that when I rebooted and didn't login (just left it on the user accounts screen), left for work, and came back, it came out of sleep mode just fine. So apparently the problem is related to being LOGGED IN. No idea what that would be though...