Merging Two Identical Spreadsheets

I have three large txt files. All three are the same number of columns but are of a different number of rows. (Each month the number of columns will increase but the 3 source files will still contain an equal number).

Therefore I need to open the first text file, select all data and paste it into my master file.

I then want to open the second txt file and paste all the data at the first empty row of my master file.

I will then open the third txt file and paste all the data at the first empty row of the master file.

Finally I will close the txt files.

I will then have several other amendments to make to the master data file.

So to my problem....

Opening the txt files is fine.

However I want to select all the data in the first txt file but excel gives me an error message. (On the line highlighted in my code). I remember there being a function in VBA that selects all data around a cell, can anyone remember how to do this?

My code so far is:

Workbooks.OpenText Filename:= _
"C:CUSTOMERPass 1.txt" _
, Origin:=xlWindows, StartRow:=1, DataType:=xlDelimited, TextQualifier _
:=xlDoubleQuote, ConsecutiveDelimiter:=False, Tab:=True, Semicolon:= _
False, Comma:=False, Space:=False, Other:=False, FieldInfo:= Array(Array _
(1, 1), Array(2, 1), Array(3, 1), Array(4, 1), Array(5, 1), Array(6, 1), Array(7, 1), Array(8 _
, 1), Array(9, 1))
Cells.Select
Selection.Copy
ActiveWindow.WindowState = xlMinimized
Sheets("Data").Select
ActiveSheet.Paste