i did loopback test on 2 arduino 1 works and other dont what to do

i have 2 arduino i tried to upload program in them but got error (Arduino: 1.8.9 (Windows 10), Board: "Arduino/Genuino Uno" Sketch uses 928 bytes (2%) of program storage space. Maximum is 32256 bytes. Global variables use 9 bytes (0%) of dynamic memory, leaving 2039 bytes for local variables. Maximum is 2048 bytes. avrdude: stk500_recv(): programmer is not responding avrdude: stk500_getsync() attempt 1 of 10: not in sync: )
i tried to do loopback test and in 1 i got response but in other rx light will only flash when i input but no output
i have tried different methods i followed different threads methods and it did not did any good to me i even tried blink program but nothing it compiles perfectly but then i get error please help

If you have any external circuitry connected to the Arduino boards, try removing that to see if the problem goes away. Make sure the boards are not sitting on any conductive objects which might short out the contacts on the bottom of the board.

If that doesn't help, I'd recommend having a try at burning the bootloaders on the boards. If you don't own an ISP programmer, you can use an extra Arduino board as an "Arduino as ISP" programmer:

I'm not sure if I would put much importance on the loopback test results. I recently gave it a try on a few different perfectly working boards and it fails on most of them. I have no clue why.