I have a couple things you can try to help figure out what is going on.
You will need PuTTY (just putty.exe).
Plug in the isostick then run PuTTY. Choose Serial and enter the COM port of the isostick bootloader. Speed doesn't matter.
If everything goes according to plan, you will just get a blank PuTTY window.
Now paste or carefully type in "CEREAL NUMBAR?" then press Enter. It should spit out a serial number 2 characters at a time, for a total of 30 characters.
Next, do, in any order:
- BOOT REVISHUN?
- HARDWARE REVISHUN?
Assuming everything worked so far, please copy down the responses from each of these commands somewhere before proceeding to the next step, since it will flood the terminal with text as part of a stress test.
[If, at this point, the isostick has failed to respond to commands or is acting up at all, go ahead and close PuTTY, then power cycle it or push the button again, and then run PuTTY again with the same settings as before.]
Lastly, a stress test. Give it the command "PUSH BUTTON"
As the meme goes, you should receive copious amounts of "BACON!" on your screen.
This puts the isostick's processor in a high power usage state, with all peripherals enabled, sending data out over high-speed USB at maximum speed. The LED should also toggle very quickly (it may appear to be steadily on).
If, however, bacon is not received, then the bootloader must be corrupt. While checks are in place at every step to prevent this sort of thing (for instance, it is not possible for the updater to ever overwrite the bootloader, or the bootloader to overwrite itself), it is always possible you ended up with a faulty processor or similar.
Anyway, I will hold off judgement of your isostick's fate until I see the results from the above tests.
Side note: the isostick bootloader's command set is affectionately referred to as the "protoLOL." Given that bootloaders must be so resilient and accordingly light on features, this was my source of amusement while writing it.