13.04 will not boot up after spindown

[John Sowden]

I used my 13.04 Ubuntu this morning fine.  I then stopped using it for a 
few hours.  When I tried to start it up (move mouse, press arrow keys, 
etc.) no action.  The screen is black( but on), the computer does not 
respond.  I tried to access another virtual screen (tried alt F1 and 
ctrl alt f1 (forgot which is right), no action. Powered down (pushed 
power sw for 20 sec. Then powered up: leds flashed on both dvd drives, 
heard a noise fan or hd?, no action on the screen.  I unplugged the vga 
conn. got a no signal. plugged it back in, black.  The only change to 
the 'system'  that I have made recently is to turn off the screen after 
a while and spin down the hd after a while (exact times unknown).

thoughts?

John

psst: is this what 'kernel panic' means?