My Dell 2407 WFPb won't stay in sleep mode when my laptop goes to sleep, even though the Dell did it until recently. "Entering sleep mode" flashes briefly, but than the Dell switches back to power-on mode, except the message "DVI-D cable not plugged in" now bounces around the screen. The DVI cable is plugged in at all times: it's a HDMI-DVI connector which worked fine as far as sleep mode until recently. I replaced all the caps on the Dell's power supply board just in case, but it didn't fix the problem (the monitor works OK otherwise, so I didn't break anything by replacing...