How To Remove //GS Mainboard?

["Marvin Miller" <marvinmiller@hotmail.com>]

Hi;

It's time to clean the living daylights out of my //gs. To that end I want
to scrub the bottom half of the CPU case.
I took everything out including the front cover with the power light on it.

When trying to remove the mainboard, I can see that you have to press out
the little plastic tabs. It looks like it must slide out through the front.
The problem is the back does not want to come out. Is there some trick?

Best;
Marvin