My old power supply died so I went for a replacement. The old one was a 250W ATX which wasn't available so I purchased a 300W ATX with alll other requirements being basically the same. After putting the new one in the computer will not boot. The fans (PSU and CPU) come on and the lights on the front come on but it doesn't POST or run the BIOS at alll. It just sits there without even spinning the CD's or Disk drive.

Did this switch in power screw something up on the Motherboard that caused this and if I go back to a 250W PSU is it repairable? I also have two cables on the new power supply that weren't present on the old one. One looks similar to a Molex connector but has 3 black wires, 2 orange and a red. The other has 2 yellow and 2 black ina square configuaration. I don't see any place where these appear to fit.

Thanks for any suggestions.

Power supplies are independent as any power supply will work as long has it will fit the case and has enough power to supply to the computer. So there are some reasons that you could be having this problem. My guess would be that maybe your old power supply shorted out and could have done damage to your motherboard. Do you get any beeps that you didn't hear before your old power supply died? The other is to make sure that all disk drive, CD-ROM's are plug up, and that the connection are ok and not just lose. Also check to make sure all cards video card and sound card as well as any others you may have are still in place and that you didn't accidentally knock one out of place. In any case if the plugs are ok and the cards are ok and tightly in place then you will more than likely need to start testing the computer components to see if maybe one of them is bad.

With the plug you asked about this is a P4 only connection and if you don't have a P4 then you don't have to worry about it.

My last power supply died its final death while booting up. It was kicking out intermittently before that. The last time it was used it had loaded Windows XP and was in the process of loading the virus scan and firewall when it went out so I really don't think it killed anything on the Motherboard but I don't know.

I've tried just about every combination of connectors and components. It's an old machine so I only have a hard drive, CD, and CDRW plus 3.5". I'll keep trying to single things out.

I'm not too sure about this strange problem. I will see if I can find anything about this on the Internet. I would suggest having the Motherboard, RAM and CPU tested. Also test the power supply itself as it could be it that is having problems.

My other computers for parts and diaggnostics are even older than this one so I don't have any other motherboards to test with. I did find my multimeter and I'm getting the proper voltages of 5,7,and 12 where I am supposed to get them so I think the new power supply is working properly.

Not having another motherboard, I finally gave up and took it to a shop with more test equipment. Will here from them on Monday. It still has me baffled that the CD drives are drawing the right power and never had their data cables unhooked from the motherboard yet they won't even spin for me.? I have to believe that something fried on the motherboard. Like you said - maybe the CPU or BIOS?

Thanks for answering

Your welcome I'm sorry that I couldn't be of more help. I hope that they can find your problem, as this one is new to me. Please if you don't mind let me know what they say so that if this happens to someone else I may be of more help.