iPhone 6 sudden death wont turn on charge or be reconigzed by itunes

Well, the failure shortly after a DIY repair could be a coincidence. This could also be caused by the original impact/drop that caused the screen to crack in the first place. It's hard to say from where I'm sitting.

I would go back through this guide and double check my steps to insure I didn't forget anything important. Things to check for are whether or not you installed the correct screws for the LCD bracket. Putting the wrong screws in can cause Long Screw Damage.

I would also try the original, cracked screen to see if that works. If it does, it means your replacement screen is defective. Finally, you could try to connect only the battery and Dock to the logic board and see if Itunes recognizes the device. If it doesn't, then you most likely have a logic board issue and that would have to be looked at by a micro-solderer.