I have a formula;

=HYPERLINK(INDIRECT($A225&"!"&"$B$4"),INDIRECT($A225&"!"&"$B$4"))

that is not working. It comes up with an error message "Cannot open
specified file".

Originally, the cell contained the following formula, but i'm trying to put
a hyperlink over the top of it.

=INDIRECT($A224&"!"&"$B$4")

This indirect statement basically returns the data in workbook / cell
'5'!B4. I want to be able to hyperlink to that.