This is a classic sign of corrupt firmware. In some cases, this is caused by a failing power adapter (providing unstable voltage), but if the hardware is fine, you may need to perform a or a hard reset. Holding the reset button for 10–15 seconds restores the firmware settings to factory defaults, clearing conflicting configurations.
If your after an update attempt, try these fixes: dlink dsl124 firmware work
: The D-Link DSL-124 uses a Trendchip TC3162U chipset with a proprietary ADSL driver. There is no stable OpenWrt build for this model. Attempting to flash non-official firmware will almost certainly brick the device. This is a classic sign of corrupt firmware