Laptop wont start to windows

Hello,
for a while now my laptop will only randomlly start up when I ask it to. When I press the power it will start the fan and come to the point where the screen is about to turn on. but fails. my laptop then keeps restarting itself and keeps trying to turn itself on properly. It seems to help if I wait a while between trying (perhaps an overheating problem?) The weird thing is that Sometimes the laptop will start as normal, and I can use it as normal. What's wrong with it?!
thanks for your help
p.s. ive tried hoovering for dust and a virus check and I restored the computer to how it was a month ago, I have also checked the disk for errors but running a scan