can you telnet into it? try this:
open a command prompt, type telnet ipaddress (it will probably prompt you for a password...unless you left it wide open)
or you can type:
ping ipaddress
You need to see if it is actually working on the network...if either of those don't work...something is def wrong. You can try a cold reboot (you will lose all of the programmed settings in the jetdirect) by powering off the printer holding the go button down and restarting the printer (while still holding the go button down). It should say Cold Reset on the screen.
Make sure you assign this printer a static IP address when you telnet into it...if you do not...every time you get a new ip address (via dhcp) your printer will become unuseable (i'm sure this is what's happened in your case). Go through the menu and print out the info sheet, and look for the ip address of the printer, and match that to your print server to make sure the two are the same.
good luck