Does wa830 work properly on your 3rd floor? Normally, to ensure a stable connection, you'd better not put a client device after a range extender.

;)Hope your problem will be solved after upgrading. Cross my fingers...^_^

It seems...faulty... Just do a hard reset and check Internet indicator... If it is off, I think it is absolutely fautly since your modem works with the old router and same cables.

You may try to disable Windows firewall and anti-virus software. Uninstall the previous software and reinstall it. Maybe it works with no error on a different PC. Anyway, it is soooooooo... weird....