My nexus 7 does not start after updating the system. It is in a never ending loop. I would appreciate any help.
Probably, something went wrong during update.
/data partition might be problematic after updates sometimes. Or it might be directly related to the system files that are downloaded during update. Try to boot into recovery mode using guides from here and here and factory reset your phone. It'll format
/data partition clean and therefore delete every user data you have on your phone such as apps, apps' datas, SMS, call logs, etc. If the problem is related to a bad/corrupted or a non-compatible
/data partition, the problem will be solved.
However, if the problem is related to other things such as bad system files or problem(s) during installation of downloaded files, flashing a clean ROM will be necessary.