A failed upgrade (due to power loss or wrong file) will leave the router with a blinking power LED and no response at 192.168.1.1 . Do not throw it away. The C1 has a bootloader that supports emergency recovery.
Complete Guide to D-Link DSL-2750U C1 Firmware Updates The D-Link DSL-2750U Wireless N 300 ADSL2+ modem router is a workhorse for home and small office internet connectivity. However, running an outdated firmware version on your hardware revision C1 device can lead to security vulnerabilities, frequent disconnections, and dropped Wi-Fi signals. d-link dsl-2750u c1 firmware
Download the latest firmware file, which typically ends in a .bin or .img extension. A failed upgrade (due to power loss or
D-Link has largely EOL’d (End of Life) this device. The official support page is sparse. However, depending on your region (Russia, India, Southeast Asia), you might find a last-gasp update from late 2023/early 2024. Complete Guide to D-Link DSL-2750U C1 Firmware Updates