help RB912 keeps rebooting and beeping

*Help me please

I have two RB912 suddenly stopped working

just working for few seconds and reboots about every 30 seconds and beeping during each reboot
*

I’ve flashed the routerboard by netinstall with OS of version 6.11 and it has worked

but two of rb912’s OS got corrupted in the same day.
is there any cause for this ?
. is there any problem with the package ver 6.11 ?

will the problem occur again?