Why doesn't Windows 7 wake up from sleep?

"Ideas for resolving not coming out of sleep:

Disconnect any and all unnecessary devices from your PC. Pare it down to the absolute minimum : unplug anything you can disconnect, turn off and unplug the computer from the mains for a few minutes, then reboot.
Look in your BIOS for the suspend ACPI options and try to switch modes among ""S1 and S3"", ""S3"" etc.
Ensure ""Allow this device to wake computer"" is checked in in ""Device Manager/$device$/ Properties/Power Management"", where $device$ stands for keyboard and mouse.
Turn off Hybrid sleep, see explanation here (for Vista, but is the same)
The hibernation file is sometimes disabled by disk cleaning, to restore do in cmd run as administrator ""powercfg -h on"".

You can use the following command to troubleshoot sleep problems and return a detailed report:

powercfg -ENERGY"

"I have been having the exact same problem with my AV Server/PVR machine (Intel MB) and spent almost a week (on & off) trying to solve it, so here is what worked for me...

Enter the BIOS and set power management to S1 - the Intel Bios warns about using S3 as some programs or device drivers do not work when set to S3 of higher.
In the BIOS - disable Wake up on LAN - I have been told that routers perform polling to see what is connected if they are in DHCP mode - this wakes the computer

I do not need to have LAN activity wake up this particular machine - so it is not an issue
seems my wireless router does not have this effect on the machine, but my wired router causes problems

Once I made these changes everything worked fine - even better than fine - since my ATSC tuner card from HAUPPAUGE wakes up the machine to record programs even from Hibernate mode, but then there is no keyboard wake-up - you gotta get out of the lazy-Boy and press the power button.

Sleep also works as required and allows for keyboard wake-up, but the fan stays on (not sure why)

Hope this helps"