Pc wont start no power, power getting through to

pc wont start no power, power isgetting through to motherboard because i have had the side of an can see two lights lit up,
can try starting it for ages nothing happens then all of a sudden it fires up.
when i eventually get it up and running i dont have any issues withe the computer it does not blue screen it does not freeze it runs like a dream.
i am just scared to turn it off cos it wont start back up again