g'day Haylee and welcome to the forums,
obviously, since you are using Outlook, it's always used PST or OST files, nature of the beast.
and as with any database file, they go pear-shaped.
not often, but enough that MS have provided a free repair tool for it.
what was the error message you were getting when opening Outlook?
you should find the repair tool in c:\program files\microsoft office\office12\ and it's called scanpst.exe
your outlook.pst file should be in c:\users\your profile name\appdata\local\microsoft\outlook
Once you find the SCANPST program, double click to run it.
Browse to the location of the PST to repair.
Click the Options button and select No Log.
Click Start.
It will do 8 phases, most of which will be very slow, depending on the size of your PST file.
If a repair is needed, untick the Make backup of scanned file before repairing (takes too long and all you are backing up is the broken one anyway) and click Repair.
Once complete, open Outlook and see if it has worked.
if you have more than one PST file (like archive.pst for example), they all may need scanning.
