SQL trigger to avoid real time registration errors

Question

hi all,
i have create a form(web app) to register customer details with "Submit" button.Once i click button "New" the registration form
will appear with new generated Account Number.after fill form click submit to save into SQL server database..
While one customer register his details another customer from other place Click button "New" to make registration.
so same Account Number will generated and build problem when both click "Submit" button at same time.
how could i prevent this problem ?
if i use locking method to lock Account Number when click "New". Is this possible?