Excel Column headers at 409 height

We have a problem with Excel 2000 column headers at full hieght at 409, as opposed to 12. But it seems to have affected the default sheet as it opens like that when opening a new sheet. Is this possibly viral activity? A re-install of Excel did not remove the issue, but copying the Office folder from Prog. Files | MS Office has removed the issue. I have macro security set to high for the moment, but a virus scan on the files that caused it has found nothing. Trying to reformat the row size makes no difference, and shows as 12.5, but remans at 409.

Anyone seen this problem before? Is it a virus?
Many thanks
Matt