I know you've fixed the problem by re-seating the ribbon cable to the sensor module - but maybe worth commenting for future use :Ctrl+u not stoping boot loader, also entered key`s are shown on screen like more than one symbol.
If you can't stop the bootloader, and what you type does not show correctly, it suggests the serial TTL connection to the camera is not wired correctly.
Is it wired like this example (camera connector is the same as the NVR)?
Hikvision NVR DS-7804N-E1/4P Bricked
Hello, i have NVR DS-7804N-E1/4P bricked when i flash wrong firmware DS-7604NI for it. So now it only boot to Logo then bip bip and auto restart. I tried flash TFTP very many time by set IP of my PC to 192.0.0.128 / subnet 255.255.255.0 and turn firewall is off. But no thing flashable although i...