I have a 2.80 GHz Intel Core i5-2300, 64 bit, Windows 7 Ultimate desktop with a modem/router as well as a router that covers the further part of the house. We have quite a few laptops.
When the trouble started, I had a Netgear DGN2000 modem/router connected with an ADSL line to the desktop and an Airlive router, also connected with an ADSL line to the Netgear. The Airlive stopped working and I replaced it with a TRENDnet TEW-736RE which from the start we had trouble with-the connection was erratic, etc. Once the next problem is fixed, I will start with that one.
Just after installing the TRENDnet TEW-736RE, my troubles started. The internet on the desktop either was very slow or there was no internet. With the help of my ISP and numerous changes in settings, we could not get any internet on the desktop. BUT, we found that with an ADSL line connected to the Netgear or wireless, I could get a good signal on my laptop.
I then bought a TP-Link TD-W8960N modem/router, but same problem persists. Good wireless to all the laptops, occasional or no internet on the desktop and sometimes even fast internet on the desktop.
With regards to the modem/router, if the light (indicated with the white line) is not on, there is no internet at all to the desktop and laptops. I usually check the lines then, but to no effect.
That light is not even indicated in the guideline:
In this case, the modem/router and desktop was off for an hour, the light is burning, but no internet at the desktop and laptop.
I have no idea what is going on. I am not sure if it is the network adaptor of the desktop, or the wireless modem/router or anything else.