Dim part As String
    Dim found As Range
newPart:
    Windows("Master Cleaned Kits Oct updated.xlsx").Activate
    part = InputBox("Enter Part No.", "Part Number Lookup")
    Set found = Cells.Find(what:=part, After:=ActiveCell, LookIn:=xlFormulas,LookAt:=xlWhole, SearchOrder:=xlByRows, SearchDirection:=xlNext, MatchCase:=False, SearchFormat:=False).Activate
    If found Is Nothing Then
        msg2 = MsgBox("Error! Invalid part number.", vbOKOnly)
        GoTo newPart
    End If
    Range(ActiveCell, ActiveCell.End(xlDown).Offset(-1)).Select
    Range(Selection, Selection.End(xlToRight)).Select
    Selection.Copy
When I run this macro, I get a run time error 424 on the Find. 
I am looking for the macro to return to the newPart: label if the number entered is incorrect or left empty so that the user can try enter the part number again.
 
    