I am assuming that your formulas are =A1&, " ", &B2 and that you just didn't include the = in your post.
The likely problem is that Excel has these cells formatted as Text and when you enter the formulas Excel treats them as a text string and not a formula.
Clear the cells.
Select the cells and format them as numbers.
Enter a number in each cell.
Clear the cells again
Enter your formulas again.
This should result in the formulas being correctly recognized.
If you post again it would be helpful if you used a title which describes your problem. It makes it easier in the future to search the forum for relevant issues.