Nexus 5 restarts after every screen lock and wifi connection does not work any longer. Who

Hi,
I downloaded Lollipop 5.0.1 a few weeks ago. When I want to lock my screen by pressing the power button or if the screen locks automatically, my Nexus 5 restarts. Wifi connection also doesn't work. I have tried the following: I have cleared cache, ejected the sim card, looked for system updates (no available), updated apps and finally I did a factory reset. These actions did not solve the problem.
Can someone help me out?

Welcome to Android Central! It sounds defective. Where did you get your Nexus 5? If it was from Google Play, then you should contact Google and see if the free replacement program is still active.