Hello cxc,
Welcome to the HP Forums.
I understand your computer is unable to connect to a wireless network since upgrading to Windows 8.1. I apologize for the delay but I will do my best to assist you.
I first want to make sure your drivers are up-to-date. You can use the HP Support Assistant to install the latest drivers. This document will provide information on how to do this: Downloading or Updating Software and Drivers for HP Computers
If that does not resolve the issue, here is some additional troubleshooting you can attempt:
1. Power cycle the entire network. To do this, turn off everything connected to the router and modem, then turn off the router and modem. Wait a minute, then turn on the router and mode. Once their functioning properly, turn on everything else that was connected to the network.
2. Disable any firewall, anti-virus or security software. This software is known to interfere with wireless connections.
3. Reset your Internet Protocol. For more information on how to do this (the command prompt command is the same in Windows 8.1), please reference this Microsoft document: How to reset Internet Protocol
4. Try chaning your computer's TCP/IP settings. These steps are able to be done on Windows 8, as referenced here: Change TCP/IP settings
I believe this troubleshooting can resolve the issue. Either way, please post your results. Thanks for posting on the HP Forums. Have a great day!
Mario