Router lights constantly blinking

I recently installed a DI-604 router, and have three PCs connected through it. The router link light showing the connection to one of the PCs which runs Windows Xp on it. The router has a password and all of their computers are turned off. I don't think the light should be flickering like it is. We are able to get the PC onto the Internet, but I have noticed that eventually our speed decreases. So, can any body tell me that why does my router lights constantly keep on blinking? What i need to do in order to resolve the above issue? Does any body knows about it? Kindly provide me the correct solution for the above issue.

According to me if your are having a wireless router with you, then it will have a light blinking on it, as it indicates the responds to any nearby equipment ion the same band. Even if only to check if its' encryption works. some systems always have a light flashing.

The first step in debugging a networking problem should not involve any of the computers. Its constantly sending data. Either you have spyware accessing the net or you maybe you use it as a file server. Often there is a broadband modem (cable or DSL) and a separate router. Rather, you should look at the lights on the box(es) sitting at the hub of the network.

You could log into the router and see if other devices are connected. Flashing lights (assuming you mean the wireless and ADSL lights) are entirely normal it just denotes that data is being transmitted. If you connect to the admin you should see the MAC address of users connected. Make sure you changed the def admin password too. If by second light you mean the ADSL light, when it turns orange it means it has lost ADSL sync i.e. your connection has dropped not good unless this is just after you've re-powered the router, when again, this would be normal.