Resecure Security on DIR-615 after reset

Hello,

I've got a really big problem I think, we were issued with a D-Link Model DIR-615 from Virgin Media, it was working fine, but we purchased a new laptop and could not get onto my wireless network as we forgot the password for the Network Authentication. My brother thought he was being helpful by resetting the D-Link and now when we go wireless it is "open" constantly and not secured. We have unplugged everything now as we don't know how to secure the wireless link at all. Any help anyone could provide would be really appreciated.

Thanks J