Outlook 2000 disappears

Running Outlook 2000 on a Windows 98 SE machine. Was working fine then after lunch came back and it was gone. Press ctrl/alt/del and it shows up in the lists of tasks running. I even receive email (message pops up) but Outlook doesn’t show up as minimized or anything (even alt/tab will not change to program). If I “End Task” on the Outlook that is open and then start the program again the Outlook screen pops up, like it’s opening, and then it disappears. But it IS running because I receive email. Any help for this strange occurrence would be appreciated.