I'm running Windows 7 Home Premium SP 1 64-bit on a HP 620 (just a year old).
Lately, whenever I return to the laptop having left it alone for some time (Power Management set to 'Sleep' after 10 mins), and try to resume, I can hear the it resuming (fans etc.), however, the screen remains completely black.
The only solution is to shut down the system manually and boot it up again.