To answer your question, this is a macro I recorded to open a series of
files in a particular order. It's nothing fancy, and I'm sure there
are more elegant ways to do this, but this is intuitive and you can
make it work for your application.

But more importantly, and this it totally an editorial so you can stop
reading now: it strikes me that requiring 50 workbooks to open
simultaneously makes your data subject to error, and is a system that
needs optimizing. Suggest a better methodology to the boss: it'll make
you look like a genius, and you'll be able to say I told you so when it
fails the next audit. Editorial ends, macro follows:

Sub Macro1()
Workbooks.Open Filename:="C:\ok2del a.xls"
ActiveWindow.WindowState = xlMinimized

Workbooks.Open Filename:="C:\ok2del b.xls"
ActiveWindow.WindowState = xlMinimized

Workbooks.Open Filename:="C:\ok2del c.xls"
ActiveWindow.WindowState = xlMinimized

End Sub