formulas stopped working

For some reason today the all the formulas won't work.

The one I use most is CONCATENATE.

I type =CONCATENATE(A1,B1,C1,D1,E1,F1) and when I hit return it just displays that same formula instead of the result. Usually it gives me the result.

I tested some other formulas, such as SUM and I get the same behavior.

Can you help me? This is really weird.

Thanks, Lisa

Yeah it was formatted as text. I changed to general and now it's working. Thanks!!!!