i9505 Stuck in boot screen after cracked screen replacement

I have a Galaxy S4 (i9505) that had a cracked screen which rendered the phone unusable (it looked like a squid had squirted ink all over the screen from within, touch still worked, but I could barely see a thing), so I bought a replacement lcd/digitiser, etc, took the phone apart, replaced the screen, put everything back together and now...I cannot get past the boot screen.

I was previously running CM12 (some nightly build from a couple of months back) and had had no troubles with it at all.
I have ClockworkMod Recovery 6.0.4.7 running as recovery and can flash, wipe, etc, but none of this works.
I've currently only tried wipe data/factory reset and re-flashing CM12 and CM11.

I'm considering flashing TouchWiz, full stock, to see if that works, but really...I hate TW so it's far from ideal.
Then again, having a broken phone is less ideal than TW, so I'll take anything at this point :)

Does anyone have any suggestions?
Have I messed something in the hardware that could cause this?

The fact that I can get to recovery and/or bootloader, says to me that things should be ok, but I'm quite confused.

Should I try flashing a stock ROM with ODIN instead?
Am I missing something simple?

Any help is most appreciated.

Patrick.