Hi Melko,
Probably you already have a solution but i found a general solution for such problems in the website of j-walk, "Excel Developer tip". The formula we use for conditional summing is SUMIF. But for multiple criteria in different fields, the SUMIF function doesn't work. However, you can use an array formula. Remember, When you an array formula, press ctrl+Shift+Enter after you write it.
For example
Sum of Sales where Month="Jan" AND Region="North"
An array is a group (a list or a table) of data such as matrix. In EXCEL you can perform certain matrix calculations with array formula. Just see help for matrix calculations.
I am afraid that is do not work that way.
I mean, if both condition are true I'll just have the sum of ALL data in the c6:c15 and not only the ones that respect the condition and if both condition are not meet I'll just hve nothing.