It may be corrupted and need to do a Boot recovery, either TFTP Boot recovery for Flash based systems or RAWWriter for USB or CF based systems. You can download stuff off the Netgear site to do this stuff. Sorry, never seen one of these devices before, just done a quick search on the web and come up with this as a possible.
There is also mention of possible DIMM memory module re-seating. Often works to sort out problems on PCs so don't see why it wouldn't be worth it on one of these.