Greetings guys can you help me with this one,

i want to validate if the username is already taken or not yet but i don't have a clue on how to do it.

i tried this code

dtCustomer.Rows.Count > 0

but it didn't work @_@.. please guys i really need help thanks in advance :D.

Easiest way is to wuery the database as in

SELECT COUNT(*) WHERE Username = 'joeblow'

If the returned value is 0 then the username is available. I suggest you use parameters to create the query string. How you do that depends on whether you are using OleDB or SqlClient. You can find examples of both here