System Agent Problem??

Syptoms: 1.Users are able to log on but cannot see any content;2.After stopping all services, one user tried to log on, the CPU usage went up to 100% and hence hung the svr;3.after moving the mailbox to another server, user are able to log on and send/rcv mails as usual. But the mailbox belong to me, which is also the service account, cannot be moved due to this error: The client operation failed. MS Xchg Svr Info Store ID no: 80004005-0501-000004b6-000004b6.
Plus, all mails in the Inbox are missing although those in the subfolders are still there.
I have this error from the event viewer: Event ID:13008, error code 0x80040115.
Thanks.