Chosen Solution

What causes the iPhone 6 plus to not boot but only show a solid blue screen ? is there anyway to fix it ?

BSOD or Blue Screen of Death is usually caused by a logic board failure, specifically long-screw damage following a repair. You don’t give us much history to go on so it’s hard to say what is wrong with your phone. Is this following a cracked screen repair, water damage, bent housing (the 6+ is very vulnerable to that). Have you updated your iPhone to the latest version of iOS? BSOD and other logic board failures are repairable, for the most part, but are not inexpensive. You need to find a repair shop that does micro-soldering repairs so that they can properly diagnose your phone and give you an estimate.