Flickering screen and data dissapears

Some of my users are using a file in excel that has multiple worksheets and bunch of formulas in each worksheet. The file itself does not have any links to other worksheets or other files nor does it have any VB scripst embedded in it.

The problem is, when a user uses Alt+Tab to switch between programs, or other excel worksheets, the screen flickers in the worksheet and the data in the cells dissapears. If you highlight the whole sheet by clicking at the box on the top left corner, the data comes back again.

This is a sporadic issue and it does not happen all the time, but it is annoying.

I have removed MS Office and reinstalled, I have formated the computer and reinstalled everything. I have upgraded the memory from 1GB to 2 GB.

This is a Dell Latitude laptop. The only thing left for me to suspect is the video card and it's an ATI Mobility Radeon 9000 with 32MB of memory

Thank You

This probably is not an excel thing but a computer issue....and more likely a monitor refresh problem...