Domain Computers keep losing connection

Hi all !

we just moved our office to a new location . we had an internal network and were sharing a T1 connection using NAT. in the new office we are using the same structure. we are sharing a B DSL line using DSL router.  we are using the same 2000 server DC. the problem is users can see the computers in the domain but when they access it , they are asked for user name and password. when they log off and log in again they are able to access other computers, but this is only for a while ..after which all users are again required to put in a username and password. evcen when they put thier username and password, it doesnt connect and says that windows has al;ready tried that username and password and could not finda domainc ontroller to authenticate that. the DC are on are working fine. I changed some stuff on DNS while configuring. all computers can ping each other with name and ip both and also to the DC. i dont know whats wrong. Please help as this is causing shared printers not to work and files not being acccess... please help ..