The device will turn on for 3 seconds and turn itself off

The reason you are finding so many different answer is for several reasons:

1) Everyone has their own opinion about what is wrong with PS4's when they do this...many of them are wrong!

2) There are several different things that can cause this problem and there is no way to know which one it is until you just start trying stuff.

Things to try:

1) The first thing to try is simply to put it up on it's side (vertically) and give it a bump on your knee or something else...I'm not saying to drop from 1ft high onto the hard floor, just give it a good bump. Sometimes this will get it working for a while but it probably won't last.

2) Sometimes this type of problem is caused by a faulty power supply. This is not common but it does happen. The only good way to test if this is the problem or not is to replace it with a known good one.

3) Probably the most common cause of this problem is faulty solder on the motherboard and bad APU chips. Some of the consoles that have these problems are fixable and some are not...the only way to tell is to try fixing.

I'm sorry I can't give you a precise answer but there are just too many variables with this common problem.

I hope it's helped