average should be 0 if it exists in the used cells?

use something like this for values in B4:B12

HTML Code: 

Either
=IF(COUNTIF(cells,0)>0,0,AVERAGE(cells))
or
=IF(MIN(Cells)=0,0,AVERAGE(cells))


where cells is the range of values used, like B2:M2. I have assumed that the values are contiguous.

Since it seems like you are learning you should write the formula and use correct cell references.
All three formulas suggested should work.

For every formula, replace all the , with ; (Commas with semicolons)

You likely use semicolons instead of commas as the argument separators, so try this:

=IF(MIN(Cells)=0;0;AVERAGE(cells))

And you may need to use a different language for IF MIN and AVERAGE - this is an English language site and English versions are assumed.