First thing to check is that you are not overwriting the database everytime you start your program - is the datadirectory a sub-folder of your project? Are you querying the release version or the debug version if it is?
Try running the following code in Sql Server Management Studio after connecting to that database using the connection details from your code.
insert into ComputerLab (LASTNAME,COMPUTER) values('LASTNAME','COMPUTER')
If any errors are reported then address those errors - you may have a column on that table that cannot be NULL but which you are not inserting for example.
Try running the stored procedure directly from SSMS
sp_insert 'LASTNAME', 'COMPUTERNAME'
and see if any errors are shown.
Do you have multiple schemas within your database? Try
SELECT * FROM dbo.ComputerLab