Employee check in and check out system using asp.net C#

hi,
I need help regarding employee check in and check out system. my requirement is when user come to office (let say 9 o clock) open a link default.aspx page a button should appear like Checkin button then in code behind i will take userid, user's pc IPAddress and date time that he come to office. Then a checkout button should appear for him when he wants to leave office (let say 4 o clock). 
Now i thought i should use enable cookie when user click on checkin button and disable checkin and enable checkout buttons and when at user wants to leave office he can click on checkout button so i can get his leaving time. but my problem is when user close the browser or clear the browser cookies after checkin i will loose cookie information. what i want here is once user click on checkin button at 9 o clock only checkout button should appears to him even though he close and reopen the browser or clear the cookies/cache. so how can i achive my requirement any ide ...