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Does your system have integrated video? If the monitors are working on other systems the problem is not the monitor but, more the video card or Windows. If your system has integrated video you may want to contact Dell Support. If you have a pci or agp video card try removing and reseating it into the slot.
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Same problem with a Dimension 4600, LCD stuck in power save. Reinserting the video card did the trick. Thanks.
Been monkeying with powersave options, another thread suggested a conflict between screen saver and power save (standby) timed settings...?