D-Link often releases different firmware for different hardware revisions. Installing the wrong one = a dead router.
(e.g., A1, B1, T1), which can be found on the sticker at the bottom of the router. Official Support Page: D-Link Support Portal D-Link Global Download Center D-link Dsl-124 Firmware Update Download --BEST
If the sticker is faded, log into the router’s web interface (192.168.1.1) → Status → Device Info → Hardware Version. D-link Dsl-124 Firmware Update Download --BEST