Lumia 1020 - Lots of issues happening at once!

[Z82]

Background
Phone: Lumia 1020 (Nokia 909)
OS: WP8.1 (8.10.14226.359)
Country: UK
Purchased: April 2014
Carrier: EE
Previous Issues: 6 month ago phone started to overheat then one day I restarted and it never came back on displaying the "Unable to find a bootable option error", EE took it back and repaired it, no more overheating and I was happy again.

New Issue

1. About a week ago I noticed I tried to unlock my phone and nothing happened, I did a soft rest and all was good... for about 10mins! Same thing happened again, and again, and again.
2. I also noticed that my phone could no longer be recognised as a drive when plugged in to USB, it opened the folder that usually shows "Phone: blah blah GB Free of Blah Blah GB", instead an empty folder saying "No Preview".
3. The 3rd issue I noticed was that the phone could no longer be shut down, pressing and holding the on/off/unlock button restarted it 99% of the time instead of shutting it down.

I did a load of Soft Resets but no joy so I decided to do a full reformat, this worked great... for about an hour, first issue I noticed is many app installs/updates were failing, then the above 3 issues slowly started to reappear, by the 3rd hour I was back to square 1.

Any ideas are welcomed as I am lost and Im pretty sure I know what EE will say when I phone them tomorrow :unhappysweat:
I

 

[Z82]

No ideas from anyone?

 

[Marlon Bu]

Do you installed any new app before these strange things happened?