White halo effect on every screen on iPhone - Any ideas?

I have recently begun to have problems with my 18 month old iPhone 5 freezing in shutdown. I have had to reset it several times. After checking all settings and deleting unused apps etc. I seemed to have resolved the problem and it has been fine for about three weeks. However, today whilst the phone was recharging it began an intermittent beeping - this stopped when I disconnected it from the charger. I then updated it to the most recent iOS 7. This evening it became very overheated (hasn't done this before) and now it is displaying a white halo effect on every screen.

The phone has not been dropped or ever immersed in water. I only ever use the original lightning cable and charger.

I have 6 months to go of a 2 year contract.

Has anyone else had this problem? Is there hope or is my phone in its death throes??

I would greatly appreciate any help or advice. Thank you.