Sum returns value 0

I just want to sum a column with cells like
=LOOKUP(D44;$Sheet1.$A$5:$BZ$5;$Sheet1.$A$95:$BZ$95)
=LOOKUP(D45;$Sheet1.$A$5:$BZ$5;$Sheet1.$A$95:$BZ$95)

etc.
and it returns zero
Obviously it doesnt recognise the data as numbers, but I don’t understand why. The number format is general…

Are the LOOKUP formulas returning zero?

Where is the sum function?