Help HTC Desire from boost mobile

[llerrom]

I have the HTC Desire from boost mobile and I'm having a heck of a time with it. Okay so the other day it started to flash the log in screen to off and back to log in screen then off. This happens at a rate of about 5 to 6 time every ten seconds; then it stalls and lets me use it, then goes right back at the same rate after about 15 seconds of phone use. So I thought that the on off button was stuck. Seemed to help when I leveraged the power button away and took my phone case off. Sooooooo when the phone gets to 55% it stops charging. But it will charge if it's off...... At 55% it proceeds to stop charging or if it's over 55%, after being off, it flashes crazily with the on off procedure (whilst plugged in to charge). Not sure if this makes sense but I think either a new phone or a backup and reset is needed. I feel like this is the weirdest problem ever. HELP!