Running Office 2008 for Mac

When I try to enter data into a cell I double click it and the cursor appears in the cell.

I then have perhaps one second to enter data before the cursor disappears and the cell returns to being highlighted.

If I do not try to enter any data the cursor still disappears and the cell returns to being highlighted.

If I keep typing data it continues to be entered however all data entered before it returns to being highlighted is lost.

Also when I try to highlight a cell if often picks a cell some rows above or below depending on the position of the cursor relative to the cell, e.g. lower egg or upper edge.

This happens in new and old spreadsheets.

I have removed the preference files for excel and MS office to try and remedy. (Excel recreates these when re-opened)

Can anyone help me please?

Thanks

Steve