Old(ish) Linux computer won’t start Up

I have an old(ish) Linux computer, updated OS, and the works, but as of the past year almost, it will not turn on. I know that it isn’t the power source, because there is a light shinning on the back of the computer, but it will not power up at all. I have tried most ordinary things that could be used to fix it (and I am quite good with computers), but I’m afraid that unless anyone on here can answer my question, I will just have to sell it or throw it out.