Lenovo laptop won't start up

Hey guys,

Since a few days my Lenovo laptop won't properly start up anymore, it doesn't even start Windows anymore. When I press the power button, the screen shows a black screen saying the white Lenovo logo, then a black screen with white text (just a normal startup screen). After this, however, it either shuts down immediately, or alternates between the two previously mentioned screens for a few minutes, and then shuts down.
It does make a lot of noise when it alternates between the two screens (a buzzing noise) so it sounds like it's at least trying to do something.

I don't really know much about laptops, so I'll just give you all the information the laptop says:
Brand: Lenovo
Operating system: Windows 7
Intel core i5
Bottom left of the screen it says U310', and bottom right of the keyboard it says ideapad, I'm guessing one of these is the type/model.

I hope someone can help me!

Ps. While typing this I've noticed that it tries to start up sometimes, without me touching it.

 

Oh, and what I've tried so far is pressing f8, f2 and f12 (suggestions from other forums). Might be good to mention the laptop doesn't have a cd drive either, since I've seen suggestions involving this as well.