Outlook 2007

I upgraded to office 2007 last week and “thought” it was doing pretty well. Until this morning. Opened Outlook and a few of my emails were disappearing before I could even read them. Like a “Ghost” in my Outlook. Have no clue what the problem is or how it started. Had a sender resend me an email three times and all three times, it disappeared before I could read it. Anyone ever experience this before and know a solutiion if they have. Thank you so much.
Carol Monson/USDA