You'll also hit this issue if the PST file is approaching 2GB in size. Outlook can't open files above this limit.

I'd suggest check the file size of the PST, if its under this size, then run scanpst see if it helps.

If the Mail icon is missing and your running Vista, make sure you are running in Classic view and then the icon should display. If your running a 64bit OS then you need to enable the 32 bit control panel using Additional Options->View x86 Control Panel menu.

From the mail icon, you can configure the PST's you wish to open (if you have to create a new one).

Regards

Matt