Computer Hope

In small office it has one server. Installed win server 2003 on the machine, it has two network card the first one is connected from router to the server, the second one is from server to the switch. And on wifi router connected to swich. it share file and internet to the client but before two weeks till now the internet stop sharing frequently  within 15 sometimes 30 minute between ADSL router. I was trying to solve this problem but it's difficult for me is there any one help me or give me information how to reconfigure again. Thanks in advance.