|Since you've updated the firmware already, the only other things I can think of to try would be:|
1) Power the unit off for about 10 seconds and then start it up again.
If this fixes your problem, you're done. If it doesn't, try the next step
2) Reset router to factory defaults (instructions will be in it's manual) and reconfigure
If this fixes the problem you're done. If it doesn't, then it's very likely your router is failing and needs to be replaced.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.