Why is my screen freezing and flickering?

I'm having this problem since the beginning of May 2010.

Turning on my MBP (or turning it on from the sleep mode), my screen shows immediately many vertical, colored lines, then it starts to flicker till it freezes; I can see my desktop with many small dots, that slightly turn to white till I'm no more able to see anything else.

I realised that moving the panel and making a light pressure near the Esc / F1 digits, it seems working again.

In my opinion it can be some kind of contact between the lower and the upper part....but which one??

Inverter? Fluorescent Bulb?...?

Thanks in advance.