Hi,
Thank you for posting your query on Microsoft Community.
I understand that you are unable to use the AltGr key on your keyboard after the update.
It would be great if you could answer these questions in order to assist you further.
1. The make and model of your computer?
2. Have you tried using the On Screen Keyboard?
I suggest you to try the methods given below and check if it helps:
Method 1: Start Windows in safe mode and see if the issue persist.
Windows Startup Settings (including safe mode):
http://windows.microsoft.com/en-us/windows-8/windows-startup-settings-safe-mode
Note: Steps for Windows 8 or 8.1 applies to Windows 10.
Method 2: Clean Boot.
A clean boot is performed to start Windows by using a minimal set of drivers and startup programs. This helps eliminate software conflicts that occur when you install a program or an update or when you run a program in Windows 8.1,
Windows 8, Windows 7, or Windows Vista. You may also troubleshoot or determine what conflict is causing the problem by performing a clean boot.
Please refer the steps given in the link below
to perform a Clean Boot:
http://support.microsoft.com/kb/929135
Disclaimer: After you have finished troubleshooting, follow these steps from section “How to reset the computer to start as usual after clean boot troubleshooting” to reset the computer to start as usual.
Hope the information helps. Let us know if you need further assistance. We will be happy to help.
Thank you.