I recently upgraded my PC with a new case, motherboard, and CPU since my old parts were outdated. After rebuilding my rig, it won't turn on at all. I first thought the problem might be the power supply, so I tested it with a tester and verified the voltage—everything seemed fine there. Next, I replaced the motherboard but the issue persisted. Then, I swapped out the CPU as well, yet still no luck. To troubleshoot further, I plugged in my old motherboard and CPU into the new case, and it powered on perfectly. With the new components, the cooler fans spin for just a second, and the GPU fans continue for as long as I hold the power button, but it won't boot even with the essential components connected: motherboard, CPU, GPU, one stick of RAM, and power supply. I'd appreciate any advice!
For reference, my old specs were: Strix Z390-E Motherboard, Intel Core i7-9700K, 16GB DDR4 RAM, Cooler Master H500P, and an Nvidia 3070 GPU. The new specs are: B550 motherboard, AMD Ryzen 7 5800XT 8-Core CPU, same Nvidia 3070 graphics card, Nzxt H5 Flow RGB case, HyperX 16GB RAM, and a Thermaltake Smart BM3 850W 80 Plus Bronze semi-modular power supply.
3 Answers
It's important to clarify what you mean by "won't turn on." Does the system make any noise, or is it completely silent? Do you see anything on the screen, or does it shut down right away? Just need a bit more detail on what you've tried and what happened for each step.
Hey, be sure to check all your connections, especially those to the motherboard and power supply. Sometimes it’s just a loose cable that can cause these symptoms. Also, try booting with minimum components outside the case to rule out a short.
Sounds like a weird issue! When you say the coolers start to rotate, do you see any diagnostic LEDs lighting up on the motherboard? That might give some hints about what’s going wrong.

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