Opening a file using a macro based on a file name held within a cell

Within a macro, I want to be able to lookup a file name from a cell on a worksheet and open that particular file. Does anyone know how I can do this?

Here are 2 examples
Chage cell refernce as required.

Workbooks.Open(Filename:=Range("a1")).RunAutoMacros Which:= _
        xlAutoOpen

Workbooks.Open(Filename:="C:\Temp\" & Range("a1")).RunAutoMacros Which:= _
        xlAutoOpen