I have had this problem on my last three notebook computers from Dell using
Excel 2007. It has been isolated to what appears to be a software problem as
it does not happen in safe mode. In addition, it does happen on the
notebooks built in screen as well as the attached monitor I use.

When I'm using excel (even )with no other program running), the screen will:
1. Flicker often
2. Text will just randomly disappear. I have to alt-tab back and forth
between another screen to get it to reappear.
AND/OR
3. Text will appear on top of itself...
4. I will have two spreadsheets open and I cannot switch between them. I
can minimze the excel screen, but that is all.

I just purchased a new dell with a discrete memory card, etc. thinking maybe
the video demands were just too much, but the exact same problem pops up.

In addition, my home PC, using excel 2007 has never had this issue - UNTIL -
I emailed one of my spreadsheets home and all of a sudden it started doing it
on the spreadsheet I sent home.

This is a brand new PC system for a company that uses good security
software, etc. Two of the three PC's this has happened on were using
different security software (one was for the last company I worked for). No
one else at my company has had this issue.

Dell can't figure it out, and of course Microsoft won't talk to you if the
software is OEM - so there's really no support for this issue to speak of.