Lanny Marcus wrote: . . .
We have four (4) Dell Dimension boxes and their support here is *SUPER*, but they use proprietary cases, motherboards and power supplies. Their quote of USD$237 for a new motherboard is probably not something I am going to follow up on. The box is running most of the time, which is puzzling, because it is an intermittent problem.
Just a shot in the dark . . . look at the electrolytic can caps on the mainboard. If any of them are "puffy" - the top is domed, not flat - that could be your problem and an easy fix. I've run into this issue on several different devices.
http://en.wikipedia.org/wiki/Capacitor_plague http://badcaps.net