Select Case YourComboBoxNameHere
Case "Form 1"
DoCmd.OpenForm "Form 1"
Case "Form 2"
DoCmd.OpenForm "Form 2"
Case "Form 3"
DoCmd.OpenForm "Form 3"
Case "Form 4"
DoCmd.OpenForm "Form 4"
Case Else
MsgBox "Please select a valid form to open!", vbCritical, "Invalid Form"
Exit Sub
End Select