active directory isnt communicating

I have a w2k3 small business server that is not allowing a system to login. when investigating problem i tryed to reset a password on a different account and it said it couldent find file. ldap has given a error about not communicating with active directory. several exchange related messages in the event viewer siad they could not contact the domain controler. the system was rebooted and I atempted to restart the varous services with no luck I have no idea what to do