I usually show the LAN port working on my laptop on the call. Then wait for them to ask me to fix their desktop.
I have belkin N300 wireless n router modem.After plugging in the ADSL line provided by ISP in the ADSL slot of the device , I am able to access Internet on WiFi enabled devices. But when I am trying to access Internet on old desktop by plugging in lan cable to one of the lan ports provided in the device I am unable to do so.How to access Internet on desktop which does not have WiFi support through WiFi router ?

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