A few days ago, I went out of town, and I thought it'd be wise to pull the plugs for my TV, PC, consoles etc., to avoid having anything be on standby and consuming (i know, very small amounts of) power.
Now I've just come back home, plugged everything back in, and powered it up. That is, except my desktop computer...
I've experienced this problem before in different situations, e.g. when unplugging the computer and changing some parts. Every time the computer has been completely without power for some time, it takes some time, after it has been plugged back in, before it will actually boot up. During that waiting period, nothing happens when I push the power button. I then leave it, and suddenly it boots up as if nothing happened. Actually, while writing this on my netbook, the desktop has booted up by itself.
Why is that? :-)