computer turns on by itself or it does not turn on at all,

So, there are different ifs?

Well, my computer is a Y540 (15inch). and this is how it turns on. I connect it… I leave it on for a few minutes connect and it might happen two situations:

a) the computer turns on by itself or it does not turn on at all, it keeps flashing the power bottom

b) I disconnect the power cable and after a few seconds, it turns on.

So, what the issue is? (My computer is out of warranty)