I'm having the same problem with a Xerox 3335. Most of the time it works fine, but every now and then when I try to print to it, it won't wake up and none of the buttons on the machine work except powering it off and turning it on again. Meanwhile on my computer it shows the printer status as "1 document waiting". My Xerox already has a fixed IP address so that doesn't seem to be the problem. Very annoying!
More data. After more time, it turns out constraining the IP to be the same did not solve the problem. Every once in a while, a PowerOnReset is still required. sigh.
I found one answer on a different thread (can't find it now) that reportedly solved the problem by manually assigning the printer a static IP address using the printer's control panel. The problem with this solution is that you must ensure that this IP does not match an existing or future dynamically assigned IP in your local network.
A more robust solution for me, on my home network, was to assign an IP using the DHCP Reservations list in my home base station. Here you are telling the automatic IP assignment program running in the router to always assign this IP to the printer (using the printers MAC address to identify it). This was quite easy in my case since it was an Apple base station and I could use AirPort Utility.
The key point though is that many of the "printer won't wakeup" problems I've noticed in mulitple threads (and I've experienced for years) are likely due to the printer waking up and getting assigned a different IP address. And that assigning it a fixed IP is the solution.
Has anyone gotten any kind of an answer from Xerox on this problem? We had a printer that worked perfectly for 10 months. Started doing this occasionally and within weeks we were having to restart the printer five or six times a day. Xerox sent a tech who replaced the network card, that did not help at all so they replaced the printer and the new printer is doing exactly the same thing. I have spent hours with tech services and customer relations and am completely fed up. They act like they have never heard of the problem.... firmware is completely up to date. Help?!?