WinForm application to keep track of errors in system.

Question

Winform Application to keep a regular track of problems arising in a system and those issues have been solved or not, if handled then which system engineer took care of it. Actually in my application there should be no role of database and all the data must be displayed and stored in an excel sheet, plus there should be a Log in and registration form . Now here the problem is i have no clue how and where to store the registered users and use them as there is no database being implemented in our tool. Any ideas or help is appreciated.......