Outlook will not open.

Are you using Outlook in a corp environment, or accessing an internet provider's email?

Trying to find out if you are using the offline file type of .OST( not .PST)

Sometimes the .OST becomes corrupted and needs to be recreated.

If the .PST main mail storage is messed up, then use the Office tool scanpst.exe which should be on your office CD, or possibly already on the hard drive under:
http://office.microsoft.com/en-001/outlook-help/repair-outlook-data-files-pst-and-ost-HA010075831.aspx

Hi Rob,  When I said repair tool I meant the scanpst.exe file.  It says it fixed the problem, but Outlook will still not open.  If you got some suggestions I would like to hear them.  This is for a client who is very angry I told him to use Outlook.

What is the size of the .PST file?

It is on the client's computer.  It is BIG!  About 2000 emails a day.  Out of space maybe?

Well...it might be too big for the normal PST file size limit.

Do you know what version of Outlook is being used?

http://support.microsoft.com/kb/982577

If at the 20G limit using Outlook 2003/Outlook 2007, an easy fix might be to just upgrade him to Outlook 2010/Outlook 2013 if he is using an older version.

See this link too:
http://support.microsoft.com/kb/832925

Use 2013

Sorry.  He is using 2013

How big is the actual .PST file?
Is he using an .OST file?

What type of email environment is the person using? Internet email or Corporate Exchange server?

It is hooked up to his gmail account.  IMAP connection.

Thanks for the help!