I have a northgate WALAMD200A, the power went down

Unplug it and wait a bit, then retry.
If it fails again:
-an internal fan might be stuck, causing the thing to shut down out of caution
-the BIOS battery might have given up the ghost
-a chipset heatsink might have fallen off and need some care
-the power supply might be toast (swap for a good spare of adequate wattage and retry)
-maybe your videocard just got unseated because of cable buggering, just set it back