Edited my post after downloading your db. You said CustRowID is name of combobox. It is not.
Records don't show because of query links. I changed to:
SELECT tblJobs.JobNo, ([FirstName]+" ") & [BusOrLastName] AS CustomerName, [tblContacts].[ConFirstName] & " " & [ConLastName] AS ContactName, tblJobs.CustomerPONo, tblJobs.JobDescription, tblJobs.OrderDate, tblJobs.DueDate, tblJobs.DoneDate, tblJobs.OfficeCopyNotes, tblJobs.ShopCopyNotes, tblCustomers.CustRowID
FROM tblContacts RIGHT JOIN (tblCustomers INNER JOIN tblJobs ON tblCustomers.CustRowID = tblJobs.CustRowID) ON tblContacts.CustRowID = tblJobs.ContactIDRowNo
WHERE (((tblCustomers.CustRowID)=[Forms]![frmLookUpJobsByCustomer]![fldCustCode]));