Agree with snart's 11/16/13 post.
My situation with a client's printer.
Deployed printer using WiFi. Worked for over a year, then about two months ago, my client reports that the printer does not work. Upon site visit found printer to still have an IP address reported in its panel, but unable to PING it from any workstation on the network. Power cycling does not return network response. Changed the Sleep mode timer, still no change. If I turned off the WiFi radio in the printer, then turn it back on, the network function returns. The workstations are able to ping the printer and find the printer automatically. Queued printed jobs print. Yesterday, I visited again to flash the firmware only to find both the printer non-responsive (but with its IP still) and the firmware already current. I tried to flash the firmware, via ethernet, but because the printer was up to date could not re-flash it. I turned off WiFi and left the printer connected to the network via ethernet and advised by client that I would post my findings and advise to replace the printer if ethernet connection fails too.
I don't have any proof of this idea, but it appears that there is a failure with a chip or component associated with network in the printer.