My computer is acting weird!

Hey there!
I’ve run into a bit of a weird one (at least in my book 🙂) with my PC, and I was wondering if anyone here might have a clue what's going on.
Basically, everything runs perfectly fine under normal circumstances. However, if there’s a sudden power outage or any kind of unexpected shutdown, the machine refuses to boot back up (even after the power comes back on 😁). It won't show any signs of life at all—no sounds, nothing. The power button just flashes green for a split second and then dies. Normally, the light stays solid green while I'm actually using it.
After playing around with the cables, I noticed something strange: if I unplug the Ethernet cable, the computer boots up without any issues. Once it's running, I can plug the network cable back in and everything works fine... until the next power surge hits and the whole cycle repeats itself 🤔
Just to give some context, this is an older setup running an Intel Core Duo CPU, 2 GB of RAM, and macOS.

Thanks in advance for the help!

A network cable shouldn't be messing with your PC's ability to boot up since everything is galvanically isolated from the machine.
Take a look at your BIOS settings first—check the "boot options" to make sure the network isn't accidentally set as the primary boot device instead of your hard drive. While you're in there, double-check the system date; if it's totally off, your CMOS battery might be dead, which can definitely scramble your settings.

If none of that works, try grabbing a different power supply from a friend or another rig and see if that gets you running.

Check your power supply—grab a known working one and stress test it for a few days.
If that doesn't fix it, you’re probably looking at a network card issue, so just try slapping a dedicated PCIe card in there...
And while you're at it, swap out the CMOS battery on the motherboard. You can pick one up at any local Best Buy or similar shop, just make sure you get a high-quality one since that's what holds your data settings.