Computer died?

So I’ve had an old Dell Optiplex 620 running for about 3 years straight now (powered on probably 98% of the time with my irc and servers :>), and it finally died. My brother said he was watching a video, then the video froze (but the audio continued) so he shut it down. When he tried to turn it back on, it wouldn’t power on at all. We dusted it, let it cool down, still wont turn on. The little LED in the case is on, so it’s receiving power (not sure if that means the power adapter is working properly though?)

Any ideas? My dad thinks it’s the power supply/adapter, any other ideas? Don’t want to buy a new one and then have it not be the issue.

If we can’t fix it it’s not a big deal, I’d just like to possibly be able to save it.

Can you swap the parts out of another computer? To test of course.