IDE Controller Failure

While trouble-shooting a “whining” noise in an old DELL (Optiplex GXMT 5133) desktop computer, the power supply was connected ONLY to the power clip on the motherboard. No other components were connected to power. It was powered up for about 30 seconds (until all the beeper were done), to rule out the power supply as the source of the “whine”.
After reconnecting all the components, the machine will not boot. It stops halfway thru the POST with an IDE Controller Failure message.
I’ve double checked the connections and replaced the cables.
Can anybody tell me what might have happened and if this motherboard is now TOAST?