notebook screen goes dim at boot

Hello, I am having a 3 years old Compaq EVO N1015V notebook. Sometimes when I boot the PC the screen becomes dim, though I can read the stuff but its very low contract. If I wiggle the screen a bit sometimes it starts flickering and at some point it gets back to normal. After this there is no issues even if I am working for long hours.

Can someone help please.

Cheers