Internet not work when connecting ADSL-Router to GB switch ?

Today, is the first time I post question publicity, coz I spend nearly one month to find out what is the exact problem but no result. I’ve tried to post in some forum but no reply with the responsive answer. So let’s help me together !
When connecting ADSL-Router to a Computer directly, the internet is working fine, accessing to ADSL-router administration interface is also OK. But every time, I connect from ADSL-Router to a Switch, from switch to PCs, the internet works for a moment, then disconnect, then I can not login to ADSL-router administration interface anymore.
  • 2 days ago
  • 2 days left to answer.

Additional Details

After figured my switch is 24-Port Gigabit Switch TL-SG1024, it is an unmanaged switch. It’s is a very unusual problem I ever met before!Today, I’ve just changed to another ISP, the problem still occurred. I don’t think it cause by Cables or missed configuration, Because these configurations (ADSL-Router and Wirelress router) works fine for me many years. What’s amazing now, I’ve replaced associated device such as new Switch, new modem, and new ADSL-router, but the problems can’t be solves.

Is it possible caused by virus or something else over my network ?

Updated : 05-04-2013
Finally, this problem is cause by some Viruses, malware or something else on my Server. After reinstalled my Windows Server 2003, the problem is fixed.

Now my office network running smoothly. What we have to think is which computer on the network are exposing to the out site network, for professional network engineer might use Network monitoring tool to see which packet running are harmful to network traffic.