If(ISBLANK)

Assuming reference blocks (cells) A1, B1, C1:

=IF( ISBLANK( A1), "", IF( AND( ISBLANK( B1), ISBLANK( C1)), "B&C
Blank", IF( ISBLANK( B1), "C1 has an entry!", "B1 has an entry")))

Assuming reference blocks (cells) A1, B1, C1:

=IF( ISBLANK( A1), "", IF( AND( ISBLANK( B1), ISBLANK( C1)), "B&C
Blank", IF( ISBLANK( B1), "C1 has an entry!", "B1 has an entry")))

I need to pull from 4 different sheets within the workbook based on whether
1,2, or 3 reference blocks are left blank. If block one is left blank then
the sum should be blank but if it is not blank then the sesult would vary
depending on whether or not one or more of the other blocks were blank or
not. each combination creats different answers. What is the best way to do
this? Thanks.

Assuming reference blocks (cells) A1, B1, C1:

=IF( ISBLANK( A1), "", IF( AND( ISBLANK( B1), ISBLANK( C1)), "B&C
Blank", IF( ISBLANK( B1), "C1 has an entry!", "B1 has an entry")))