Okay, you've tried everything else, now give this a try: After each step, put the machine into standby and then see if you can wake it up.
1) In your power settings, tell the HDD never to power down.
2) Set your video adapter driver from Geforce to Standard VGA.
3) Go into your system properties, hardware profiles and copy your original configuration, naming it Test or something. Reboot and select the test configuration. Now for the scary part - go into the device amanager and start disabling stuff, everything but the video, HDD, mouse, and motherboard resources. Reboot, go into standby, and see if that fixes it. If it does, go to , if not, start disabling Motherboard resources one at a time, rebooting, going into standby, etc.
Begin enabling devices, one at a time, and booting into the test config. When the system hangs on standby again, you have found the problem device, and can boot into your normal configuration, disable the offending device, and get on with it.
Oh yeah, don't forget to delete the test configuration after this is all over.