Hold down the power button untill it reboots.
Else hold down the power button and volume down at the same time until it reboots
Try for longer time up to 1 min per option.
You shoot be able to boot the into bootloader.
From there you are able to use:
Nexus root toolkit from WUGFRESH
NRT_v2.0.4.sfx.exe
Make sure to select the right Device and Android version you want to use.
this has a option Restore / Upgrade / Downgrade
With option Sorft-bricked / bootloop
Use this one.
Hope to be of help
Last edited by Boeli; 2015-04-07 at 10:18.
Reason: For got time
Nexus 4 and Nexus 7 2012 other harware Odroid U2, PI 2 running kali, Kali on Ironkey and laptop and server