PS4 fixed now, but don't know what the problem was!

Hey guys, I tried searching for this problem, but all I'm getting is the similar PS4 shuts off issue.

So I got a new PS4 from Amazon Warehouse deals and I set it up and it worked just fine. I left it on then and it switched itself off according to the power settings. So far so good - and I hadn't played any game on it yet.

Next morning however, I switch it on and for about 3-4 seconds it light up blue but then switches back off. I try again and again but no luck.

Next morning before I send it back to Amazon, I try another thing - I take out the power cord and plug it back in - and voila, it works perfectly. I can't reproduce the fault now either.

My question is, do you guys know what it is, and should I send it back anyway?

Thanks a lot! :)