It is no need to pay anything. I just want to help you.
So, try another USB tumb drive with LED (to see if there is activity). Be sure the software level to be between pounds ( # ) like this sw#07203000409100#.DLM. And be sure the AltBoot to be written with A and B in uppercase.
Checked with two tumb drive (1 and 2gb). LED flesh. Tried with firmware WorkCentre_7200-system-sw#07203000409101#.DLM and also modify the name in sw#07203000409101#.DLM . No success! replace hdd with one NTFS formatted. AltBoot written ok.
Does the Software Upgrade window appear on the UI? If not, is possible to have an broken Board or SD card (located on back of the board on the upper right corner, and this is not an ordinary SD card, it is a XEROX part with some information's on it). Send me a PM with your Email, please!