If you have replaced your ram latly it might be the ram and it could have destroyed your motherbord. This happened to me a few weeks ago, and i'm still trying to get my computer to work. It's problems loading Windows 2k pro. The power was off too, and the cables unpluged from the wall. This is just in case you replace your power supply, and power switch and it still doesn't work.
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All blades cut, be they made from metal or wood, but the sharpest and deadliest blade is the one of knowledge.
An Archmage of the HADB