Ok thank's for your help! What happened today it was that when I powered on my nexus it restarted. I don't have programs opened because I don't have time to interact with it!

(sorry my English)

It's the original nexus with android 4.2.2!
Can I format my nexus without lose my guarantee? And if I can, where can I find the OS 4.2.2? Could be a solution of my problem?

Hi! Could someone generous help me, PLEASE?
 If I have some open pages on chrome and change between them quickly, my nexus 7 reboots...not always but happens constantly, maybe 3 or 4 times a day!
Or, If I have some programs running happens the same... I think that it happens when I try to do something quickly!
Have someone with the same problem?
Thanks. (sorry my English)