iPhone 5c doing stuff all by itself - Power switch/audio control cable at fault
My daughter's iPhone 5c was doing things like screenshotting, locking, turning off and back on all by itself. Battery power would go down from 100 to 67 or so within 2 hours without anyone using it; battery is new. All the symptoms seemed to be related to the power button.
With ifixit's clear, complete instructions, my 14-year old daughter replaced the Upper Component Cable by herself as I read her the repair guide steps and pointed out a few of the hardware locations clearly pictured in the guide. The UC Cable is the ribbon cable with the power switch and volume control switches on it. It was a complete success. It wasn't hard in the least, but it took us two hours. The iPhone works correctly now.
This repair, like other iPhone repairs, involves removing an assortment of screws, shields and components. I used 1x2" zip-loc bags from Jo-Ann Fabrics to contain the parts removed at each step. I cut 4x6" note cards into 1 by 1 and a half inch pieces to insert into each bag, written on with exactly what steps the parts were removed at and where in the phone the parts came from. It eliminates confusion and makes the repair a breeze.