SBS 2003 need quick fix on dns

i have small bussiness server 2003 with local domain controller with 5 user working fine.. all of the user when they login they get drive F drive mapped from server to them automatically by DC.. only issue i am having is when they leave there computer logged in overnight there computer do not see DC i mean loose all access to the server with mapped drive but everything locally still works. The only way i have solved it is reboot the worksaton every day in morning so when i look at the error log all the pc get the same error FIRST ERROR Event Type: Error Event Source: AutoEnrollment Event ID: 15 2ND ERROR Event source: Usernv event 1053 (Userenv)Windows cannot obtain the domain controller name for your computer network. (The specified domain either does not exist or could not be contacted. ). Group Policy processing aborted." EVENT ID 1053 - Module: userenv (at logon) (someting like) I THINK THERE SOMETHING WRONG WITH MY DNS SEi have small bussiness server 2003 with local domain controller with 5 user working.. all of the user when they log inthey get drive mapped to them automatically by DC.. only issue i am having is when they leave there computer logged in overnight there computer do not see domain i mean loose all access to the network but everything locally still works. The only way i have solved it is reboot the worksaton every day at 7:00 so when i look at the error log all the pc get the same error FIRST ERROR Event Type: Error Event Source: AutoEnrollment Event ID: 15 2ND ERROR Event source: Usernv event 1053 (Userenv)Windows cannot obtain the domain controller name for your computer network. (The specified domain either does not exist or could not be contacted. ). Group Policy processing aborted." EVENT ID 1053 - Module: userenv (at logon) (someting like) I THINK SOMETHING WRONG WITH MY DNS SETUP I DO NOT KNOW WHAT IT DID.. SO NEED HELP SOME WHO KNOWS WHAT THEY DOING Also I just setup one more server just like it with 1 user just want to make sure DNS setting is ok there too. MAX IS $120.00