Check fuses. It may just have a blown fuse in the power supply or on the motherboard. It also may just be an issue with the power button.

That said, I haven't had a PS1 in years. Modern emulators like DuckStation can even play real discs but give you all sorts of benefits like upscaling, correction for polygon/texture warping, modern video outputs, etc. I regularly play my PS1 games, but I do so via an emulator on my Steam Deck.