PC wont turn on out of sleep mode

I bought the PC prebuilt off facebook marketplace, and the guy said all of the parts he bought were new or used. The PC works perfectly well, it has a 3070ti, i5-13600KF, 1x16GB RAM (installed in slot 1), 1TB SSD, and 850W PSU. I've played games on it and everything works great.

The day before yesterday, I put it in sleep mode and couldn't turn it back on out of sleep mode, but eventually I tried just hitting the power button once and after 5 seconds it all powered on (So I had some trouble but then it worked).

Then, yesterday I put it in sleep mode before work, and now I can't turn it on out of sleep mode no matter what I try. The only thing I see is the power button blinking/flashing, and when I press it, nothing happens, and it just keeps blinking.

I've tried waking it up with different keyboards and mice (both wired and wireless), but the wired mouse, when plugged in, doesn't have the red light underneath on, so I wonder if the problem is that the USBs are unpowered? The power button isn't helping either.

Does anyone have advice on how I can get my PC on?