I've heard of Window locking up but not a monitor. It only has one purppose to display whatever is in the outgoing signal from the video source. If it seems to stick in standby mode it may be one of two things either a defect with the monitor itself or the power management options in the control panel.
With a failing supply you would notice unstability with the system if it runs at all and the eventual lack of enough power to start up the system. A bad video card on the other hand usually results in an audio alarm at post where you would hear one long beep and two or more short beep codes. You would want to look over the power options to see how those are set.
