Monitor won't enter standby mode, displays Self Test instead

I have a Dell Dimension 2400 with a flat panel monitor (model number E172FP with 1280x1024, 60Hz resolution) and recently when I turn my computer off the monitor goes into a Self Test mode instead of entering standby mode like it's supposed to. The Self Test window also appears when my monitor is supposed to enter standby mode after 20 minutes to save power. The screen goes black and the graphic in the following link appears (except is says DELL Self Test Feature Check instead of DELL 1:D-SUB Self test feature check or DELL 2:DVI-DSelf test feature check). The Self Test box then slowly moves across my monitor, bouncing off the edges like some sort of screensaver.

<ADMIN NOTE: Broken link has been removed from this post by Dell>

My brother recently installed a 3D graphics accelerator video card (one using Radeon 9200 SE technology) on my system for gaming and the Self Test has been coming up since the installation. I tried disabling the Intel 82845G/GL/GE/PE/GV Graphics Controller that came installed on the computer in case the monitor was getting confused by having multiple video cards enabled but that hasn't made a difference. What can I do to get my monitor to go into the power-saving standby mode like it's supposed to instead of this Self Test thing? I'm getting really tired of having to turn my monitor on and off every time I use my computer. Thank you!