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I was told my power supply was bad so I replaced it and decided to upgrade the CPU from four to six core. When I try to start it up no lights on the I/o board, no start-up sound. Nothing just the red led light as soon as I plug it in. Tried a smc reset, zap pram, but nothing happens. The cpu was from a known working MP. Short of tearing it down and replacing the original CPU back in any ideas, suggestions? Thank you.

Hi From the photo provided I have notice the light is beside the ram so maybe try removing all ram except one stick and trying to power it on if still no luck try a different stick ,my iMac had a ram stick go bad and it had a solid light and the exact same symptoms as your Mac Pro I hope all goes well Any questions please ask Thanks:)