mobile

Hi all, after some modding it seems that my nexus 7 2013 lte custom recovery is vanished. I've tried to flash it via adb, I've flashed the new 5.1 official image, but nothing happen. Every time I try to boot into recovery mode, via adb or power+volume up, all I get is a dead android robot logo with no options.
And, btw, my N7 works perfectly
What can I do?
Thanks :)