My screen won't do anything while it's charging, can't slide to unlock or type in pin code. It just stays locked until I unplug it from the charger.
Well there is no stock setting to make it do what your experiencing unfortunately so there's no magic box to go check or un-check. What will likely happen is when you go to or call Sprint they are going to make you do a factory reset. Before that happens I'd like to make some suggestions.
Try these 1 by 1, don't just do them all at the same time cause if it helps you won't know which fixed it.
1) Try a different cable, just to eliminate you're current cable from having a grounding issue.
2) Remove any lock pattern or codes you have in Menu>Settings>Security. Plug the phone in and see if this helped at all.
3) Uninstall all of your applications you've downloaded. You can just go into the market and uninstall them. Write down the names of the free ones you have so you can download them again at a later time. All your paid ones will stay put in the market attached to your name. Plug the phone in and see if this helped at all.
4) If you've done all of the above and it still didn't help, beat Sprint to the punch and try a factory reset. This is going to wipe out your data (contacts etc). Menu > Settings > SD and Phone Storage > Factory Reset.
That's all i can think of. if someone else has something feel free to chime in.