Thanks for your reply Rory, the code is:

Sub PerformActivities()
Dim ws As Worksheet
For Each ws In ThisWorkbook.Worksheets
If Not (ws Is Sheet1) Then
Range("A1") = 1000 'Replaced my code with this line
End If
Next ws
End Sub

For some reason the macro does not go to the next worksheet (even though it says next ws). Any idea why is that?