Fired -Salary and PTO updated by someone using my access information

My hourly salary was updated and my PTO days were changed last night but not my me. Someone used my credentials to make these updates and I was promptly fired today. Everyone in the office knew where the binder was located that contained names and access information. It was only this week that the binder was put into a safe place. The office is very small approx 6 people. I've worked for the President for 4 years and have always been told I’m her right hand. Now my integrity and reputation is ruined. They can't prove I did it and I can't prove I didn't. Payroll did not process with the update and the changes were reported to my manager and I was then fired. I believe someone set me up. But I can’t prove it and I am beside myself with grief.
Do I need a lawyer and can I sue?