You haven't specified any error but i think you are getting error because of query
your ID column in DB is of integer type and you are sending it like string
Change it like this ==>
String thisQuery = "INSERT INTO abc (ID, Name, ContactNo, Email, Address) VALUES (" + txtid.Text + ", '" + txtname.Text + "', '" + txtcontact.Text + "', '" + txtemail.Text + "', '" + txtaddress.Text + "')";
Or if your ID column is identity(ie autoincrement field) then no need to send it in query
String thisQuery = "INSERT INTO abc ( Name, ContactNo, Email, Address) VALUES ('" + txtname.Text + "', '" + txtcontact.Text + "', '" + txtemail.Text + "', '" + txtaddress.Text + "')";
This is not a good practice to send parameters to query like this way as there'll be a greater chance of sql injection so yo should always use SQL Parameters to send to query