Black Screen - Help Needed Please ASAP!!

Hello,

I have a dell laptop (Vostro 1500)
When I switch it on, it goes to a black screen, with just the cursor visible. It is frozen and will not let me do anything. It won't even go to the log in screen for me.

Can anyone tell me what is wrong or how to fix it?
I have a feeling it is something to do with the HD, but I am hoping I am wrong cause I do not have anything backed up :(

Help please someone