gateway mx7515 laptop wont start up, keeps shutting off itself

so as the title says when I turn on my laptop after about 5 seconds it turns off and about 2 seconds later it turns on by itself again shuts off again after 5 seconds. While the laptop is on for those 5 seconds the LCD screen is absolutely black and you cant see anything at all even if you connect it to an external monitor. This is the first time this has ever happened to me. I leave my laptop on all day I don't turn it off unless I have to. I have my laptop set up on a desk. It does let the fan run and it isn't blocked. I've had my laptop set up in my desk for two years I never really move it unless I travel. My laptop does get really hot but I usually ignore it and I've been doing so for the last two years so I doubt that's the problem. My battery is charged so that's not the problem. Oh and when I woke up this morning my laptop was on but completely frozen I couldn't move anything so I had to shut it off by holding the power button. I tried letting the laptop cool off for a couple of hours and using a hair dryer to blow inside the fan I thought it would cool it down. I also used a vacume tube to suck out all the dust on the fan area and yet I still get the same problem. So if anyone has any suggestions that would be great thanks