Outlook 2003 Problem

Every time i open microsoft outlook 2003 it comes up with the message – The data file “Personal Folder” was not closed properly.The file is being checked for problems.

After the file has been checked, you can’t do anything with it(outlook) jst freezes. When you close it and restart the application again it tells you the same thing and goes through the same process again.What could the cause of this problem?Please advise.