Why isn't my phone turning on?

[AC Question]

Hello guys, I got this LG note f100s. when I purchased it 2nd hand it was working fine but after few time it restarts automatically and then one day I woke up and device was just getting restart again and again on logo. I gave it to market and he said, I've installed the software and after few time your device will be working fine. I don't know what is wrong with it. Its not a hardware problem I think but when I connect it with pc, I heard a sound of connecting some device but nothing happens on the screen of the phone. please help me out, thanks.