It sounds like the lock master reset might have been inadvertantly pushed when the coverplate was removed at some point. I would suggest you remove the batteries, reinstall them and reset the lockset and enter in new pass codes (you can use the same ones as before, if you wish).
I've attached the owner's manual, just in case you've misplaced yours, so you can reprogram the lockset and have the instructions for future use and reference.
http://www.smarthomeusa.com/Products/ED1460XXXX/manuals/WeiserLockPowerbolt1000-manual.pdf
Just so you know, Weiser and Kwikset were once the same company and offerred the same lock under both names, so don't worry about the manual having the Weiser brand name on it.
Hope you find this Very Helpful - Best regards!