Suddenly can't connect to NETGEAR57 (2.4), only NETGEAR57-5G (5.0)

[DFA9]

I powered down the router (unplugged for 1 minute) and powered back up.  Now nothing connects to the 2.4 (SSID NETGEAR57).  Android devices not a problem as they connect fine to the 5.0 (NEGEAR57-5G).  However, Kindle devices are still trying to connect to NETGEAR57 (2.4) and get "Authentication Problem" error. There is no way to "override" the Kindle to connect to the 5G.  It finds the 2.4 when it scans for networks and only tries to connect to that. It does not "see" the 5G.  

Nothing in my setup has changed.  Using the defaults that came with the router and have been for 2 years.  I upgraded with latest firmware (V1.0.1.4_1.0.52) and rebooted mulitple times.  Tried changing the password also.  Nothing works.  Is it time to replace the router?  

[DFA9 · Accepted solution]

WNDR3400v3. I did the factory reset and now all seems ok.  The only thing that changed after the reset was the channel on the 2.4 went from 9 to Auto.

[StephenB]

Try a factory reset, and re-apply all the settings from scratch (that is don't reload a saved config file).

[DFA9]

How do I do a factory reset? I have no disc.

[StephenB]

You don't need a disk.  Usually there's a small hole where you insert a paperclip.  After the reset you'd go through the factory reset process.

Can you tell us what router model do you have?  

[DFA9 · Accepted solution]

WNDR3400v3. I did the factory reset and now all seems ok.  The only thing that changed after the reset was the channel on the 2.4 went from 9 to Auto.