One thing you can do is you can create the table in your database with the columns as follows:
1. UserName
2. PCName
3. Date
In UserName Column you save the UserName, in PCName Column you save the PC-Name and in Date Column you save the datetime when the user logs in you application. So this will help you to keep the track on the users and their PC-Name and on which time they have logged in you appliaction