I am trying to get SUMPRODUCT to work and it is not.

Here is my data
A L M
1 C 354.54 Notes about account
2 W 16.54 Blank (Null)
3 C 154.40 Notes about account
4 NE 1.50 Blank (Null)

I am trying to get a total dollar amount (L) of all Regions (A) with notes
on account (M) and without.

Here is my formula:
=SUMPRODUCT((Detail!$A2:$A12440 ="^C"),(Detail!$M2:$M12440
=""),(Detail!L2:L12440))

I am getting "0" now. If I play with the formula, change , to -- or *, then
I get numbers, but they are not correct.
Can you help?