ok i was able to fix this issue. In case anyone encounters the same exact issue, this is what went wrong and what was made in order to make everything work:
1. make sure fastboot recognizes your device, by typing in command line "fastboot devices". if your device is not listed, first fix this (check drivers and connectivity). i had to reboot my pc in order to communicate with my nexus.
2. now boot to fastboot by holding vol up + vol down + power button.
3. launch NTK and simply select "back to stock" and check "soft brick \ bootloop" option.
4. the app with download the image and afterwards everything is automated. you will reboot to the setup screen.
BIG thanks to WugFresh and his awesome tool Nexus Root Toolkit v1.8.6.