Vostro 1320

I had the laptop for about 18 months now, it was working perfectly until I got  Dell to come in and changed the mouse pad for me, then they had to come back and change the motherboard twice as it did not work properly.

Then I got a new laptop and stopped using it, recently I opened the dell up again, but I am now having a black screen or very very dark screen, but I can see the laptop is working?

So what is wrong now.