If you are using Delphi TComPort VCL for some Arduino programs. Please set FlowControl -> ControlDTR to dtrEnable. Otherwise, you will get nothing from Serial Port.
It costed me one afternoon for this issue. I worked with a Arduino Pro Micro (Leonardo). The Serial Monitor of IDE worked well. Putty worked well and 'Serial Port Utility' worked well. Arduino Uno was tried. It works well....... Only my Delphi program couldn't get anything from the Serial Port. At last, I noticed the example program of TComPort worked well. But if I deleted this VCL and added again, it would fail. At last I found this Properties.
I don't know why. All the documents said Leonardo didn't use DTR pin.
If you have any suggestion, please let me know. Thanks a lot.