Depending on the UC Software Version, pressing the key combinations from the beginning will not work.
Note that if you press the "Setup" button when the auto-boot screen pops up, it'll go to a password screen that looks identical but where every attempt to authenticate will fail.
If it's an F for example, there will be no feedback that you've switched from d, to e, to f, just know that you have to hit it 3 times.
I bought 2 Polycom IP 5000s on e Bay for quite cheap but they were both bricked by the previous owner's phone provider. For the 3.x phones, when you first power up the device, you need to press the "About" button.
I ran into a similar problem with some Polycom sets but it was much more gruesome because all of the authoritative details on the web didn't work.
We had three Soundpoint IP 550s, one Soundpoint IP 331 and one Sound Station IP 5000.
I just want to contribute that this line right here "BUT DON'T LET GO", enlightened the hell out of me.