Let's take the usual cable modem -> PC connection. That connection is locked to the MAC ADDRESS of that old network card in the PC until it's changed by the ISP according to their rules. Some of them are simple such as power down the cable modem for a minute.
But your post left out the details so all I can share is this.
Bob
I just bought a new laptop, a Toshiba Satelitte A135. It is setup for wireless, but I will be using a regular router instead. I unplugged the ethernet cable from my current pc and plugged it into my laptop instead. The laptop showed that it was connected to a network, but there was no internet access. How can I fix this?

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