Phone will not power off but will perform a restart.

I replaced the screen recently. The phone was dropped on a concrete floor while in a case but received to visible damage. Soon after this the power button stopped working. If the power button is held down the phone will not power off. However, the phone will perform a simple restart by hold the power button and home button. In addition, the charging port must be loose as when a cable is insterted is cycles from charging to not charging unless the cord is in just the correct position. (Yes, I did try cleaning the charging port.) The phone will charge, but now seems to drain power more rapidly.

What do you think is the most likely cause of this? And the least invasive repair? (I had lots of difficulty getting the LCD and Digitizer connectors to sit properly. And I feel if I have to disconnect them again, I may ruin all of my work.) Although, i don't mind having to "crack it open" if I needed.

Thank you for your help.