can't open device "\\.\COM5": The system cannot find the file specified problem

Hey guys, so recently i bought a new arduino nano, and when i connected it with my pc, and tried to upload the code, this error showed up,
avrdude: ser_open(): can’t open device “\.\COM5”: The system cannot find the file specified.

Problem uploading to board. See http://www.arduino.cc/en/Guide/Troubleshooting#upload for suggestions.
weird thing is that, while connect my arduino uno board, it works fine, the code successfully uploads, but when using my nano, that error shows up,
also my port option is also greyed now.
i would really appreciate a helping hand.
thank you
( i also provided a screenshot)

What is the port according to Windows device manager after you connect the board?

It's unknown..

Do you mean that device manger shows an "unknown device" after connecting?
Original or clone?

If it's an unknown device and it's a clone, you probably need to install the CH340 driver (inspect the 16-pin chip at the back of the board to check if it's a CH340). You can download it from the Chinese site. Install without the Nano connected.