Router chokes and won't allow updates

> The router won't recognize the serial number [...]

   "won't recognize" is not a useful problem description.  It does not
say what you did.  It does not say what happened when you did it.  As
usual, showing actual actions (commands) with their actual results
(error messages, LED indicators, ...) can be more helpful than vague
descriptions or interpretations.

   Are you trying to say that you're using some web browser (on some
computer/device or other), trying to work with the router's management
web site ("routerlogin.net", or similar), and you can't get logged into
it (probably because you're not using the right user name and password)?

   And now you're getting stuck in the (probably defective) password
recovery procedure?

   If so, then a settings reset may be the only practical solution.

   Visit http://netgear.com/support , put in your model number, and look
for Documentation.  Get the User Manual.  Read.  Look for "Factory
Settings" or "Reset".

> [...] the router chokes regualry and we have to restart it at once a
> day. [...]

   Again, not a particularly helpful description.

   If you're not running the latest firmware, then a firmware update
might make sense.  It's worth a try, assuming that you can get into the
thing.  If that fails to help, then a previous firmware version might be
worth a try.  Some people still prefer V1.0.9.42_10.2.44 to many later
versions.

   Visit http://netgear.com/support , put in your model number, and look
for Downloads.  (For older versions, under Firmware and Software
Downloads, look for "View Previous Versions".)  Find the kit(s).
Download the kit(s) you want.  Read the "Release Notes" file for
instructions.  (In the User Manual, look for "firmware", and,
especially, for a topic like "Manually Upload Firmware to the Router".)