Today my Nexus-5 suddenly turned off and since then it doesn't load. When I turn it on it keep restart itself over and over - sometimes I can see Google is logo for one second and it restart it self again, sometimes I can see the three circle but again only for one second and... restart. I was trying to press on-button + volume-down, the phone is entering this mode but restarts it self after one second! My battery is full! I did not download anything or saved anything. Please advise. Thanks.