I too have a Central that has no display or activity when I attempt to power it up. Honestly my problem sounds very similar to this.

The kicker is that there is no display to know what is happening with the unit.

I have attempted using the boot disk and replacing the hard-drive to no avail.

There are several LED indicators on the board that may be useful however as I am not sitting in front of it right now I have no idea what is happening.

Honestly this unit has been sitting in my closet collecting dust for years since it started acting this way.