I own a d-link router, and i have a problem....the status light is always flashing, never stable...is this normal? the connection seems to be ok, but i have some problems with messenger(instant disconnection) and various online flash videos which stop buffering....thanks in advance

Yes, the status light indicates activity so it is normal for it to flash.
First, the obvious, it is possible that some of the videos are damaged...moving on...
Router troubleshooting:
It is a good idea to disconnect the power to your router for at least 30 seconds every few weeks. You should also do this to any hubs/switches between your computers and the router. Logon to router and try to set the MTU to 1492. Make sure only have one router between you and the Internet. Many ISP's refer to bridges and routers as modems so it is hard to tell. If your router connects to "modem" to access the Internet try connecting your computer directly to the "modem". If that works better then you have multiple routers "Natting". (Google: double nat) Finally, try a different router.
Computer troubleshooting:
Scan your computer for problems using Malwarebytes.org. Install all available "messenger" updates and fixes. If you are referring to Windows Messenger it has been replaced with Windows Live Messenger which is a free download. (Google: Windows Live Messenger)

I recommend that you start with the easiest recommendation to follow and, if necessary, continue to the next easiest. Don't try to do everything at once.

If this helps, please vote for my solution.