Over the past couple of days have had at least two instances of Toad not responding to the minimize control on the MDI window. The windows-M key would not minimize it either. Bouncing Toad solves the problem.
So a moment ago had the same issue and found the "PC has awakened from standby or hibernation" dialog box that had opened under Toad. I allowed it to reconnect to all of the disconnected sessions which closed the pop-under message. However, Toad would still not respond to the minimize control.