Handza have you had this problem for 7 months? (I see no other posts by you since 09-13-2007)
Have you been able to get logs from just before the services stop?
/var/log/zimbra.log, /opt/zimbra/log/mailbox.log & zmmailbox.out if you have one.
Are you still on 4.5.4? Might be time to upgrade to 4.5.11 or 5.0.5
Please post the output of:
su - zimbra
zmcontrol -v |