System will not even turn on the power supply when the “Power On” Switch is pushed.Power supply & CPU fans & case fans stay off.Had a bad lightning storm.System was off but plugged into a UPS. UPS still works with other PCs.No obvious burn marks on the system or power supply .5V power LED standby power was still working.Power On Switch was checked & OK.New power supply installed but system does not power up (no fans running).
Since the board won't power up, try a jumpwire solution to start it through the ATX power supply connector. Green wire on ATX power supply connector to ground. You may have a fried connection to the power on line, and it can be anything from a blown resistor to a fried copper trace within the motherboard (which is multilayered)
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This can be a power supply problem or a motherboard problem. One or the other has probably gone bad and must be replaced, if this is what happened. Start by disconnecting all things from the motherboard except the CPU and memory. If the system starts, then you've ruled out the power supply, CPU, motherboard, and memory. If not, remove the memory and see if it tries to start. If so, then the problem is the memory. If not, then it's definitely the power supply, CPU, or motherboard.
I know, this is a very frustrating situation... Unfortunately, the only reasonable way to find out what's wrong is to swap components with a reference system, until you found the defective part. I hope you have another P3 system available to swap parts.
I would do it this way:
First check that the power button is connected correctly.
Swap the memory from the faulty system to the reference system.
If ok, put it back into the faulty system and connect the power
supply from the reference system (or some other known good one) to the
If this doensn't help, swap the CPU from the faulty system to the reference system.
If the CPU is ok, the motherboard seems to be defective.
If you've installed the cpu and hooked the fan to the power supply plug, which is just left of the cpu mount, then the board if connected to the power supply cables, it should start up. Regardless of the front switches. However, you probably don't want to start plugging in the power cord until you have all of your components in place and ready to close up the case. First you can create a shock by just touching the board and that can damage the board. (I speak from my own experience :-( .
But once you get the power switch plugged into the board that should take over turning the rear power supply on and off (Including the cpu fan)
Good Luck and don't forget to leave a rating, based on my solution.
The way that I solved the problem was to unhook each and every connection to the motherboard except for the 4-pin and 24-pin power supply connections, the processor, the cpu fan and the power on switch connectors, once I have done that, then I plugged in the power supply and turned it on, in which that worked! After that, I would hook everything up to the motherboard one piece at a time, in which after each piece I would turn the power supply on again to see if that was the problem. Starting with the hard drive, the memory sticks and then the DVD drive, and found out that was the problem. The cable between the DVD drive and motherboard was the wrong cable for that motherboard. I will purchase a new cable and see if that works!
Either the new power supply you purchased is not functioning correctly. But, assuming it is now that you are getting some form of power to your PC, it is very likely the motherboard. Whatever fried your old power supply (or it could have just been the power supply itself) most likely fried your motherboard in the process. Probably not the CPU since the MB can't even post.