Display and audio issues

I've recently come across a new issue on my laptop, and it's something that has only started recently.
As I have no wifi at the minute and I needed to download a few things, I took my laptop in its bag to my step dads shop to use the wifi there. The laptop bag was on the back of a pram, and it tipped up, meaning the laptop - in the bag - hit the floor. It all seemed fine, I plugged it in and got to downloading. After a while, the display and audio turned off, but the fan was still spinning. I had to hold the power button to turn it off as sleep wasnt working, and it worked normally again after this. Later that day when I got home, it did it again, and it's done it a few times since. Yesterday, I took the back off, removed the HDD and the ram, cleaned any dust out from underneath and put it all back together. It was fine for a good few hours, then it happened again. I'm hoping this was just a case of the HDD coming loose, as it's not the one that came with the laptop and it doesnt screw down into the hole provided.
Does this sound like a loose connection issue, or could it be something failing? With how tight money currently is I cant afford to go buy a new one just yet, is there anything I can do to stop this happening again?