Numeric keyboard not working when using Excel in my mac

Hello:

I have a macbook pro and the number pad won't work when using Excel. Letters all work and num pad works fine everywhere else -power point, word, google chrome, safari, etc. I have tried pressing shift-clear, but nothing happens. I also tried fn F6.

Any advice would be much appreciated. I'm desperate, as I can't use Excel.

My Macbook Pro 13": OSX Yosemite 10.10.1, 8GB, 2,3ghz Intel Core i5

Thanks!