The push button to reset it should have reset it back to factory defaults of no security and default password. Only way I can see the password not working is either #1 someone who is stealing your internet sees your connection drop and come back on and quickly went in to change the password or #2 your device has been compromized by being Hack Reflashed to have a password other than the default.
If you seriously cant get back into your device to lock people out and the default password is not working, I'd get a new wireless router. If it has been hacked with a Black Flash someone could be using the logger feature to steal info between your home system and wherever you go on the web. Known as a Monkey in the Middle Attack! If your password was left as default they could have remotely flashed it on you from anywhere in the world.
If your device does seem to act as if its been flashed to not have a default password that is oem for that device, I'd seriously junk it, and check your online banking etc once secured under a new device without the default password.
The other issue to mention is that if this is an older device it may have been out there long enough for Black Hats to find a vulnerability with it. Its rare for a networking hardware device to be flawed especially from Netgear, but its not impossible. I had some 6 year old routers that I replaced a short time ago because I found it unusual that they would lock up almost as if a DoS attack and they were Linksys SR41's. Both routers in a matter of days had the same issue of broadband internet down yet the broadband modem was happy and blinking like crazy as if there was traffic, and the devices non responsive to local admin. I find it rather strange that 2 devices of the same make and model also using different power packs kept locking up tight. So I replaced them with newer units with more security features and the problems were gone. The newer routers also support IPv6 in addition to older IPv4 addressing.
