My PC suddenly powers off with no warning or blue screen. I took it to a repair shop, but it worked normally while they tested it. At home, it seemed to work after switching from a power strip to a wall outlet, and it also worked with a different strip. However, it has started failing again, and now it powers on for about a second before shutting off. The monitor only loses signal, while the outlet itself has power. This has been happening since I first got the PC, so I'm wondering whether the power strip, power supply, case power button, or something else is responsible.
3 Answers
Since the computer starts for only a second and then immediately turns off, the power supply is a strong suspect. A faulty case power button or its wiring is also possible, but the shop should test both the PSU and the motherboard. Bring the PC and the power strip back to the shop and ask them to test the system under load using a known-good PSU. Also confirm that the wall outlet works with another device.
This doesn’t sound like a storage-space problem. Running out of drive space can cause Windows errors or poor performance, but it normally won’t make the entire computer lose power instantly. Check the PSU first, then the case power switch and motherboard connections.
The different behavior between the power strip and wall outlet suggests unstable power or a failing strip, but a new strip can still be defective. Once the hardware is working, consider using a properly sized UPS with voltage regulation for the PC and monitor. A UPS can help with brownouts and power fluctuations, while a basic surge strip offers much less protection.

It does turn on for about a second and then shuts off. The outlet has power, and this has happened ever since I got the computer, so I’m starting to suspect the PSU.