I'm very new to PC building and have reached the point where I may need to take this to a repair shop. My original power supply seemed faulty—it failed the paperclip test and made an unusual noise—so I replaced it. Unfortunately, the computer still won't start with the new PSU. The 24-pin motherboard cable and 8-pin CPU cable are connected, the other plugs appear secure, and I've reseated the RAM several times. I also cleared the CMOS, replaced the case power switch, and confirmed that the motherboard receives standby power. The new PSU passes the paperclip test and its fan spins, but pressing the power button produces no response. Is there anything obvious I may be missing, or could the original PSU have damaged another component?
5 Answers
Strip it down to the minimum setup: motherboard, CPU and cooler, one RAM stick, PSU, and nothing else connected. Disconnect drives, USB devices, extra fans, and expansion cards. Test each RAM stick individually in the recommended slot, and inspect the board for shorts, loose screws, burn marks, or damaged connectors.
Try starting the system without using the case power button. With the PC unplugged, check the motherboard manual for the two power-switch pins, then briefly touch those pins with a screwdriver while the PSU is connected and switched on. This rules out the case button or an incorrectly connected front-panel cable. A photo of the motherboard wiring could also reveal a misplaced connector.
First, confirm that the switch on the back of the PSU is set to I rather than O, and that the wall outlet and power cable are working. Since the motherboard’s standby LEDs are lit, it is receiving some power, but that does not guarantee the system can start. Reseat both ends of every modular PSU cable and make sure you are using only the cables that came with the replacement PSU.
RAM usually causes a no-display or diagnostic-error situation rather than absolutely no reaction, so it may not be the main issue here. Check whether the motherboard has diagnostic LEDs or beep codes, and make sure the CPU power connector—not just the large 24-pin connector—is plugged in securely.
The PSU fan spinning during a paperclip test only shows that it can switch on; it does not prove that it works correctly under load. Still, if the replacement has enough wattage and the cables are correct, the motherboard, case wiring, or another component could be the actual problem. A failed original PSU may also have damaged the motherboard or another part, especially if there was a fault or unusual noise.
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