Mac Mini won't turn on

I was updating Leopard from 10.5.2 to 10.5.8 on an Intel Mini. (The mini wasn't connected to the internet for a few months.) The update downloaded, I clicked restart now, it started installing. Mid-update, I walked away for a few minutes and came back to check progress, but the Mini was OFF.

Weird. Why would it turn off? Did the update complete? Who knows...

So then it wouldn't turn back on! The power button did nothing.
I did the PMU/SMU reset as outlined here: http://support.apple.com/kb/HT2622 but still nothing.

I tried unplugging the brick, a different outlet, a different finger on the power button, nothing! Any ideas?

It's about 12-18 months old. It was whenever 10.5.2 was released, since it was never updated. It was being used as a video presentation in an office.