root suddenly became read only

Dear All,
I have a problem in promox ve 3.1 using kvm running ubuntu and zimbr. recently in root partition became read only so I must reboot it and running fschk upon booting, I'm facing problem from where to locate the error since the guest became read only so there's nothing in the log, can I figure out from the host for this kind for error, what kind of clue that I must to find to solve this problem

Thank You for your help

Regards,
Samuel Sappa