I have an Acer Extensa 5220 running Windows 7, and around a month ago it started having problems when attempting to enter sleep mode.
The screen dims to black nicely like it always does, however the laptop will clearly still be running. The fan is still on, and the HDD will still be accessed.
Further, the wireless mysteriously switches off (an LED turns on to indicate it's off). Logging back in, a flip of the wireless switch easily turns it back on.
I'd like to clarify that this doesn't seem to be a case of the laptop going to sleep normally and then waking up instantly (due to e.g. a device waking it up) -- although that might be the case.
Pressing anything on the keyboard turns the screen on instantly, with the character I just pressed showing up on the password input field, further showing it's awake the whole time.
I've tried many fixes, including disabling media sharing and powercfg settings, to no avail. The problem irritates me so much as I have to shutdown the computer every time instead of a quick sleep/wake procedure.