Mouse pointer & new page icon??

[Chrisjwalker]

When I open a workbook file it opens fine, but when I go to the bottom of the page and select a different worksheet tab the mouse pointer gets what looks like a "blank page icon" next to it and Excel locks. I can still move the mouse around, but can not do anything. Not even close Excel. Trying to do that gives me a circle with a line thru it. The only way I have found to exit is to start Task Manager and tell it to stop Excel. Even it comes back and says "Can not end Excel", but a few seconds after that I get the "This program has stop responding" message and Excel closes. It works fine until I try and select a different worksheet from what was originally opened when the program started. Any ideas? This is a new problem and I have not see this before yesterday.