tried this but got the error in serial monitor "Board at Null is not available".
checked cables -ok
used usbasp to program arduino uno r3 --completed successfully with progisp and hex file
what could be the issue?this is common for both windows8 and ubuntu20.04.
Turn on Verbose in File --> Preferences.
Try uploading the program then use the 'copy error messages' button and paste it here in this thread.
Loopback test is about USB/serial transceiver. It is not about the main UNO chip ATmega328P so trying to program it via ISP does not help. Maybe you have just created another problem.
USB/serial transceiver on genuine UNO R3 is ATmega16U2 or CH340 on Chinese clones - usually.
Be sure you have driver, device visible in OS an then carefully follow the instructions for loopback test, and then provide some output and more details like terminal type.
If you are sure that loopback test failed, something is probably damaged in USB/serial transceiver or power circuit.