I have been experience this problem for a long time. When I want to put my laptop into sleep mode or hibernate, it just stuck with a blank LCD but back light keeping on and CPU running in full speed, it can not go on to sleep, or go back to working state, the only choice is power off, that is rude.
I been looking for help on internet but not much valuable clue could be found, seem no body met this problem, I have to address it myself.
There is another phenomenon for my case: I am using Gb Ethernet adapter for internet access, not wireless connection, each time when the computer can’t not enter sleep mode, the GbE could not be shutdown, both indication LEDs (power and network linking status) for ether is blinking. That mean, the ether refuse to sleep, I think that is why the whole system been.
So I check HP driver update center, there is an update about ether net driver update, description mentioned some power management issues update. I checked my original driver, that is form Microsoft. So I update the HP driver (Realtec, version 7.25.824.2010), now it work fine for me. That is great so I don’t have to trun off the computer when I leave and wait for a long time to go back to working mode when I back.
My running OS is window7 32bit.