|And the problem isn't the router because two other computers are connected to it. |
And these other two computers connect wirelessly as well, or are they connected via a network cable to the router?
If the others are wireless, you will need to check and ensure the wireless interface on your problem laptop has the most up-to-date drivers available. If it already does, or you update them and that doesn't fix the issue, you will next want to try un/reinstalling the TCP/IP stack on that interface.
If neither of the above works, the next thing to do would be to remove the wireless interface from Device Manager and then reboot and let Windows "find" the device and reinstall it.
If none of the above fixes the issue, you're going to have to take it in and have a professional look at it as you may have a bad network interface.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.