What causes Outlook to not startup is a damaged .pst file which is the inbox database. When Outlook can't read this file it will not launch.
There is a repair tool given but it is not an easy thing to do.
Microsoft has tech articles for this and lets start with how to avoid this problem. This is very simple to avoid total loss of the .pst file which contains all your sent and received emails. The way to prevent total loss is backup!
Microsoft has a backup tool for versions 2007 , 2003 and 2002 which can be found at:
Instructions on the use of the tool is at:
http://office.microsoft.com/en-us/outlook-help/using-the-microsoft-outlook-personal-folders-backup-tool-HA001087532.aspx
If you depend on your email then backup every day. Make sure Outlook is closed before you run the backup.
Having a good backup is a must for Outlook since Outlook's database can be damaged very easy with no ability to recover it.
Outlook comes with a tool to repair the database but it's not 100% guaranteed to fix a damaged .pst file and it's not easy to use.
When launched it only has an input box where you are expected to enter the name of the .pst file including the location.
Most people have no clue where this is and to me it's quite surprising Microsoft has not made this easier for people.
Don't be surprised if it can not fix your file.
If that happens you will need to dekete it or replace it with a good one which is either from another PC or backup.
If you copy it from another PC you will need to erase all emails and folders and be sure no rules are setup.
They have provided a article on how to repair a .pst file which is located here:
Hope this helps.
