I am getting a 404 webpage not found error when I try to get to a list in sharepoint. When I look in Sharepoint designer I notice that the dispform and editform.aspx forms are missing. Is there a way to restore these? When I try to add a new one I get an error message that the form already exists.
Did you try deleting them before adding the replacement pages? If not try that. If you can't find them in SharePoint Designer open your page in SharePoint Manager 2010 and try to delete them in there.
Something else you could try is deleting the List and creating a new one. If you can't just delete it because of its content create a ListTemplate (that includes the list's content) from that list before you delete it and restore it afterwards from your template.