No Auto Shutdown

I have built dozens of tower systems spec approx:
AMD 1.2 upto 1.8, 20/40 gig HDD, on board AGP and modem/lan, 128/256 Ram, you get the picture = pretty much up to date specifications.
All have one thing in common Windows 2000.

My Problem isRecently i have needed to build a couple of flat desktop models, same spec (new cases and PSU)
BUT and i mean BUT, when shutting down i have to hold the button in for about 5or6 seconds to switch off, the towers switch themselves off, my users (BLESS THEM) are used to this so it is a problem when they resort to unplugging from the wall just to switch off!!!

What am i missing is it a software config?

HEEEEEEEEEEEELP