Excel formula not working

Excel formula not working

=IF(F5=0,[E5-E5*$H$1],[F5-F5*$H$1])
I have 2 columns of data that can be used and I want the calculation to
take data from the first column only when the second column is blank (I
didn't know how to add blank in so have opted for =0) and then perform the
calculation referring to a fixed reference cell.
So if F5 is blank then take EF into the calculation referring to H1 as the
fixed reference (5% is in H1). Information in columns E&F are manually
input prices, E column is normal retail price and a figure only appears in
F column if the item is selling at a reduced price.
I want one calculation in column G that takes the most current price and
works out -5%.