A suggestion for avoiding future problems:
ASSUMING you really mean "Outlook", and not "Outlook Express":
1) Make periodic backups of your Outlook .PST file (assuming you aren't on an Exchange Server). PST files can get corrupted. I suggest storing the backups somewhere BESIDES on the same computer.
2) Write down your Server connection settings (Server name, account name, password, etc.)
Recent versions of MS Office have a "Detect and Repair" option that can fix minor problems. Re-installing Outlook is also pretty easy.