Why does screen go black on laptop?

I know very little about repairing computer software problems

and this is made worse because I'm trying to help my step-daughter

over the phone with her malfunctioning laptop.

The problem started this morning when she called and said her laptop

would not start, it only showed a black screen. The little "green" lights on

the keyboard were lit as if the computer was turned on, but no desk-top

showed itself, only a black screen. She pressed the power button a number

of times, on and off, and it finally came to life.

Then another problem.

This time the Internet browser would not connect to the Internet.

After a number of times, it finally did.

Now she called me this afternoon.

She walked away from the laptop for a number of hours

but left the computer "ON".

But when she returned, once again the screen is black

and no amount of "pounding" on the separate keys on the keyboard

will bring it back to life.

Anyone familiar with this type of problem?

Thanks for any and all help