volumn problem

I use Centos 7.1 , the path /files mounts to the /dev/sda2 , but it can not be mount now.

I tried

  1. mount -a
    the system will be hang when mount to /dev/sda2

  2. xfs_repair -n /dev/sda2
    it returns no error.

The problem is solved by using the centos source disc rescue mode , but would like to know what is the cause the issue .

the partition table corruped ? system file lost ? hardware bad sector ? or other reason .

what error the centos source disc have fixed , it have overwrite the paritition table ?

besides , my system is safe now after such repairing ? is it good to re-install it or do the fully hardware diagnostic ?