Backup Issue with 5S

Hi there!

Recently I decided I didn't like IOS 9. As I am sure you are aware, you can't downgrade to ios 8 so I decided to do it the 'complicated way'.

I downloaded an older version of the software version on my phone (version 8.3.1) and followed a tutorial to add that to my list of backups on my pc.

I did this, then put my phone into DFU mode. I then plugged it into the computer, and synced it with itunes to restore it to the backup.

It didn't give me the option to use my new backup, so I just put it back to the old one, however:

Now the screen is black and wont turn on. The computer responds when I plug my phone in (itunes opens up, although there is no device recognised).

The LCD Is working but the screen is just black, nothing is changing.

At the moment I am leaving my phone to run out of charge to see if that will make a difference, do you have any advice on what I should do?

I am not covered by insurance and the phone is roughly 6 months old. I am very keen not to buy a new phone though, as I do not have much cash atm.