Bummer.
To cut a long story short, I'll get to the juicy bits!
Firstly check the hardware. Hold down D when you boot up until you see the hardware test logo. Do the tests.
If this does not fix it, you could go into internet recovery mode, with a view to doing a fresh install.
When you boot up, hold down Command (⌘) – Option (⌥) – R and keep that held down until you see this logo
(hope that shows on this post)
It'll do a bit of a load up and then will ask you for your Wifi password.
Once in there, run the disk utility and see if it can fix any problems. If this does not work, reboot and do the same routine and get into internet recovery mode.
Since Lion, there are no install discs but they do allow you to restore your mac to whatever it shipped with using the internet recovery tool. basically, you can download a fresh copy of lion and it'll install that (overwriting all your data) and hopefully will make the world well again.
In my case, I couldn't not install anything because the date and time were wrong. I needed a bit of help sorting that out but when the date and time were ok, I went onto the next step.
In my case, I downloaded and installed a copy of Lion onto an external hard drive. (it's an option in the installer) I then booted into that external harddrive (hold down the option key - it'll show your two hard drives with an OS on it). Once booted from the external hard drive, the original hard drive was visible and I was able to grab all the files I needed and copy them to the external hard drive.
Once the files were safe, I formatted the original internal hard drive and rebooted into internet recovery mode, downloaded a copy of Lion and installed it. (with the external hard drive disconnected). lion installed and I was back in action.
After all this, I was given a link that I followed that allowed me to install OSx Sierra and from there I installed High Sierra.
Then attached the external hard drive and copied back the files that were needed!
See how you get on and I'll PM the link to OSx Sierra if you need it! Good luck.
edit here is that link that allows you to update lion to sierra
https://itunes.apple.com/us/app/macos-sierra/id1127487414?mt=12