This is a calculations formula that has 3 states:
1-When field1 is not blank, but others are blank, it has one special formula.
2-when field 1 and field 2 is not blank another formula,
3- when 3 fields are not blank an other formula. it is important to treat the blank fields not as zero.
I have changed my conditional formatting, Instead of Is blank and Is not blank I have used Does match pattern and Does not match pattern, in the conditions. the custom pattern is: .+ (any character) (one or more)
I dont Know exactly why, but now it works and show the result value correctly after deleting any values. Thanks for all and hope to be useful for others!