If file exists, run a particular macro, if it doesn't, look for another file

I have 6 files that all have a separate macro run on them on a daily basis.

Rather than running them all individually, I want to run one macro, that will kick start all the others.

However, of the 6 files, 1 or 2 may not be there every day and therefore I need to be able to bypass the search for them, if they are absent.

e.g.

Files are located in
C:\Documents and Settings\My Documents\

named:
Book1.xls
Book2.xls
Book3.xls
Book4.xls
Book5.xls
Book6.xls

If Book1 is there, run macro "A", else, if Book2 is there, run macro "B", else, if book3 is there, run macro "C".......and so on.

Can anyone tell me how I go about writing this?

Many thanks

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