I would recommend doing it step by step until you find out when it stopped working. Here is my suggestion:
– Update to firmware 2.1.7, pop out microSD card, test to see if it reboots.
– Then pop in microSD card, try again
– Then import configurations, try again
and so on. If it reboots right in the first step, then it has to be a firmware problem itself (and has nothing to do with microSD card either). In any case, this allows you to find out what causes the reboot.