hello,
scp [C:/Users/my_comp_name/Downloads/AntMinerS3-cgminer/cgminer]/cgminer root@[Ip_to_antminer3]:/usr/bin/cgminer
I see. The slashes need to be backslashes for Windows. And now I see you have cgminer in the path twice. Make sure that is correct. It depends on how you unzipped the file. Try "C:\Users\my_comp_name\Downloads\AntMinerS3-cgminer\cgminer" or "C:\Users\my_comp_name\Downloads\AntMinerS3-cgminer\cgminer\cgminer" if cgminer under subdirectory cgminer.