This code  should work on whichever sheet is the active sheet, so it
should run on all of them. Unless what you want is for all the sheets
to be processed in one run of the macro? In which case (untested):

Sub hide()
For each ws in activeworkbook.sheets
Dim rw
For Each rw In ws.UsedRange.Rows
If rw.Cells(3) = 0 And rw.Cells(5) = 0 And rw.Cells(6) = 0 Then
rw.Hidden = True
Next rw
next ws
End Sub

It needed a Dim statement for the ws which I put in before the first
line of code, but when I ran the code  it got stuck on the first sheet
and was looping continuously. The debug highlighted "Next rw" and
yet this worked ok when I was only running my code on a single sheet.

Yes I did mean that I wanted the code to start with the first sheet
and work through every sheet in the workbook.

Could you help  a little more with this.

This works(tested):

Sub hide()
Dim ws
Dim rw
For Each ws In ActiveWorkbook.Sheets
For Each rw In ws.UsedRange.Rows
If rw.Cells(3) = 0 And rw.Cells(5) = 0 _
And rw.Cells(6) = 0 Then rw.Hidden = True
Next rw
Next ws
End Sub