Pc wont load on screen.

Ok. So I have my aunties computer I got from her last weekend. She said it had a few viruses etc the usual stuff which I can remove. I take it home and for some reason the display just does not work. It has a gpu have tried it on there but still only get a black screen on the pc. I know the board is working as a green light comes up and well the psu must be working as everything goes. It's a very old pc so will need to dust it and as usual its a bloody HP my number one hated brand due to the fact they make everything themself. I have switched the ram every possible way and checked the cmos and still no enjoy.

Can any of you fellow redditors help me make this pc post?