[Q] i9505 Somtimes boot, sometimes doesn't.

I had an S4 in for LCD replacement, everything went fine. Possibly the EASIEST phone repair possible.
The phone was reassembled and worked fine, put it up for sale and updated etc. After a few days of it sitting there I went to turn it back on and it wouldn't boot, just hung at the Samsung logo and wouldn't boot recovery.
I left it and thought i'd sort it the next day and went to proceed to flash with Odin until the battery charge logo came on so I knew it was working and then I turned it on and it all worked fine.

It was working fine so I thought it was a one off so turned it off and it happened again. Now im constantly flashing via Odin to try and get anything out of it, sometimes it will boot up get past the Samsung logo then it will freeze.

I have read near enough every threat on the subject, I doubt I'll get an answer here but I'll keep this bumped everyday in hope there's somebody who knows what's going on.

Here's what I've tried
- Flashed latest rom via odin
- Flashed 4.4.2 via odin (supposed to fix this issue)
- Flashed PIT & latest rom via odin
- Flashed PIT & 4.4.2 via odin

I don't know what else to do