Try below code
I will recommend to use error handler while using vlookup because error might occur when the lookup_value is not found.
Private Sub ComboBox1_Change()
On Error Resume Next
Ret = Application.WorksheetFunction.VLookup(Me.ComboBox1.Value, Worksheets("Sheet3").Range("Names"), 2, False)
On Error GoTo 0
If Ret <> "" Then MsgBox Ret
End Sub
OR
On Error Resume Next
Result = Application.VLookup(Me.ComboBox1.Value, Worksheets("Sheet3").Range("Names"), 2, False)
If Result = "Error 2042" Then
'nothing found
ElseIf cell <> Result Then
MsgBox cell.Value
End If
On Error GoTo 0