If your internet is behaving erratically, the first step is checking the firmware version.
Perform a factory reset. With the device powered on, press and hold the physical Reset button for 10 seconds, then release it. This clears out the NVRAM partition entirely and forces the new firmware filesystem to generate clean, uncorrupted default configuration templates. You will need to re-enter your ISP credentials and Wi-Fi configurations after this step. Summary Matrix: D-Link DSL-124 Firmware States Firmware State LED Indicator Behavior Root Cause Resolution Normal Booting Flashing Green/Green Cycle Decompressing Kernel and mounting filesystem. Wait 60 seconds for completion. Stable Operation Solid Green Power / Flashing DSL & Wi-Fi dlink dsl124 firmware work