Microsoft SBS/exchange/pop3connector/outlook 2003-help

Please could somebody help. I have just joined a small firm that use the above systems for e-mail. The domain is hosted on the server itself and the problem is this. For two days no incoming mail has been received and one desk can not send or receive. The guy that did this job previously has left suddenly and I can’t think of anything else to try. All the addresses are set up properly and the pop3 connector is running. Should I set up the Outlook accounts through Control Panel on each individual computer. Can pop3 connector and exchange run together as suggested in the Wizard.
I have been on this for two days now and seem to going round in circles. Any help I can get would gratefully appreciated.
Thanks and kind regards to you all!