Mine used to do this because it had a power supply affecting virus.
Scan yerself.
( Reid got it going on like Donkey Kong, Mon 4 Jul 2005, 8:21, archived)

Will do
But Macs don't get viruses :(
( The Coast Of Yemen, Mon 4 Jul 2005, 8:22, archived)

Could've been a power cut?
.
( Reid got it going on like Donkey Kong, Mon 4 Jul 2005, 8:22, archived)

No - having watched War of the Worlds a couple of days ago
I was a bit worried, but the lights work (plus the screen was still on)
( The Coast Of Yemen, Mon 4 Jul 2005, 8:25, archived)