Every once in a while the screen on my laptop goes blank, i.e. disappears completely. Neither moving the mouse nor clicking any keys gets it back. Sometimes shutting the lid & re-opening gets the display back, but on other occasions I need to hold the power button to restart from scratch, which may work on the first try, but not always.
When it doesn't work, I can hear the start up sound, but the screen is still black so I can't enter the windows password to log on & so have to start all over.
I don't know if it's related, but it's recently been suffering from an overheating problem (I've hoovered inside & out, and got it on a cooling pad to no apparent effect).
It's a slightly decrepit Acer Aspire 5735Z with Vista
Before I even got to that bit of your post the word 'overheating' was shouting out at me!
If you're sure the vents aren't blocked then either the fan isn't functioning properly or the thermal compound which binds the processor to its heat sink has failed. (Check that the processor is securely mounted).
Thanks Buenchico, I guess I'll have to take the back off again & have a proper poke around. At least if it is related to the overheating, hopefully it'll be an easier fix than taking the screen apart (I'm a master at stripping tech down & not being able to put it back together!).