Hi, and welcome to the Apple (user-to-user) Community.
Re: wifi has stopped working
Wondering if your MacBook Pro has been updated to the newest compatible MacOS available, for the security:
Eg: Identify your MacBook Pro model - Apple Support
says "Newest compatible operating system: OS X El Capitan".
I see you are using that OS, but do not know which version.
You can check from the Apple menu (in the top menu bar) > About this Mac
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If you have the newest El Capitan version 10.11.6 already installed
Seems there was a MacOS El Capitan version 10.11.6 Security update:
Apple Support's Security Update 2017-004 OS X v10.11.6 El Capitan - Apple Support has a down;load link.
Sorry I don't know whether the 2017 article's link is still working or not.
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Re: "Is there a usb adapter for a 2008 17" / "that would be able to give the laptop wifi?"
Sorry I don't know. (Some providers used to sell a small USB modem-like gadget to use in a Mac port).
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It may be possible that you do have wi-fi ... but the browser installed no longer works / connects to Internet. ?
Eg: If you use Safari it may no longer be a supported / secure version.
Firefox browser's system requirements are now for macOS 10.15 or later only.
There may be other browsers that are lightweight enough and can be used.
Apple Support's articles may or may no longer be helpful:
Wi-fi
If you can’t connect to a Wi-Fi network on Mac - Apple Support
Troubleshoot joining a Wi-Fi network on Mac - Apple Support
Resolve Wi-Fi and Bluetooth issues caused by wireless interference - Apple Support
If your device has network connectivity issues, check for VPN and other third-party security software - Apple Support
Internet:
If your Mac isn't connecting to the internet over Wi-Fi - Apple Support
Solve Internet connection problems on Mac - Apple Support
All the best :-)