Same problem I used to face a lot with installing through winbox.
Start Netinstall with your routerboard SHUTED DOWN - NO POWER at all.
PRESS the RESET button of your RB (RouterBoard) and KEEP it pressed.
POWER UP the RB while KEEP PRESSING the reset button.
DON'T LEAVE the reset button UNTIL
Netinstall "sees" your RB.
If it doesn't "see" it, RE-DO the same until it does.
AFTER it "sees" it, LEAVE the reset button.
Install the ROS once again via Netinstall.
After you SEE the finished intalation - REBOOT your RB.
When done, you will be able to "see" it with the winbox.