Hello stuby, welcome back to the forums. I would disconnect the external drive just to check whether that is causing the issue first. I'm not a MAC person but my suggestions are checking to see if you're Norton product is set to perform network scans. More overly, what boot time scan setting do you have (if its available for MAC) ? If the setting is present set it to normal. An aggressive setting does cause issues on SOME Windows machines so I'd think it could be similar for MAC.