What to do when ur computer screen goes black after u turn it on?

I have a hp compaq nw8440 and the screen goes black after i turn it on it wont even go to the login user page. I have no recovery disk and no knowledge of computers what so ever. Im trying not to pay money to get it to the store but that is my last option. I'm trying to find a way to get the labtop working withot paying anything if u have any suggestions that would help. Thankyou