The bigest question to me is: Why are the characters i typed in the HyperTerm on PC-Side are displayed on Amiga screen (what is good) and the characters i typed in NComm on Amiga doesn't send to PC or cannot recieved from PC.
I can't remember why this happens, but I can tell you for sure that it's an issue with hyperterminal. I've been through this issue many many times, and it's always related to crappy windows hyperterm. I first had this problem when I was using hyperterminal to connect to a small microcontroller board for development. I eventually got it working after tons of tweaking the baudrate in both the control panel and hyperterminal. I also had to close and start hyper terminal a bunch of times before it would go online correctly. The problem was exactly as you describe.
Make sure CTS/RTS, etc, is set correctly (off or on) in the control panel too.
Do you have all of the documentation to AExplorer? THe readme describes how to set up the serial ports (if I remember correctly). I did this on several Amigas a years ago and it worked perfectly, but I think there was a slight difference if you has older roms... I can't remember. I'll check it out.
In short, verify that the null modem cable is wired correcly, and then keep messing with hyperterminal until you get it working

tom