When I go on vacation, I unplug my computers.
The time before last when I got back, one machine wouldn't boot. After a couple of days I got around to trying to fix it, but it was fine.
I just got back from vacation again, and again it wouldn't boot. Based on what happened the first time, I just left it plugged in and kept trying it. After 1 1/2 days it started up normally.
FWIW it's an old Elonex Exentia: http://www.theregister.co.uk/2003/11/26/elonex_exentia_media_center_pc/
Any obvious causes and remedies?