What you need to do is go to the 4000 site listed on many threads on here and download DERT. Load DERT on a computer, and follow the directions that should come in the zip file.
This process requires that you either have a power supply for an Optiset Analog adapter, or you have an Inline POE power injector.
Basically you statically set the IP on your computer as indicated to 192.168.99.1 with subnet 255.255.255.0 and leave the default gateway and DNS blank.
Use a CROSSOVER network cable.
If you have the Inline POE power injector connect one end of the crossover cable to the PC and one end to the IN on the power injector, then take a regular LAN cable and plug it into the OUT port on the POE power injector.
If you are using the Optiset Analog Adapter power supply plug one end of the crossover cable into the PC, and the other end into the LAN port on the phone (not the PC port in the middle).
Start DERT and turn on DHCP and TFTP
***** NOTE - I had to edit this, I made an error....
Now, and this will be a fun experience, (If you are using the POE power injector) Hold Down the 3 key on the phone and plug in the remaining end of the network cable. The diplay will light up - as soon as it says "Staring Netboot" you can let go of the 3 key. If you set everything up correctly you will see DERT download software to the phone and then it will rebooot. After it beboots it should come back up to normal. If so, you are done. It takes less time to fix the phone than to set all the crap up!!!
If you are using the Optiset power supply you have to hold the 3 key down and plug the power supply into the RJ11 power supply jack on the bottom of the phone.
Sorry for the incomplete information - I am absolutely psychotic at work lately.
Don Bruechert, Voice Comm Analyst II
CareTech Solutions @ Holy Family Memorial
Manitowoc, WI, USA