Phone reset after screen replacement

I have just replaced an iPhone 5 screen and its working perfectly. However when i turned on the wi-fi, the screen changed to an apple logo and factory reset.

I have a backup of the phone before i changed the screen so i'm not worried about data.

But this iphone 5 hasnt been used in a while, it has an old IOS, there's no sim card inside and this would have been the first time it has connected to the internet in a long time.

Do i do an update and restore? Have i damaged something internally? is it an apple security issue? phone provider?