After update to El Capitan the keyboard doesn´t work

Have you tried resetting the NVRAM? How to Reset NVRAM on your Mac - Apple Support

When resetting the SMC did you follow these instructions to the letter?

1. Shut down the Mac.
2. Disconnect the MagSafe power adapter from the Mac.
3. Remove the battery. (Learn about removing the battery in MacBook and MacBook Pro computers.)
4. Press and hold the power button for 5 seconds.
5. Reconnect the battery and MagSafe power adapter.
6. Press the power button to turn on the Mac.

1. Choose System Preferences from the Apple menu, then select Language & Text.
2. Select Input Sources.
3. Select the Keyboard & Character Viewer checkbox.
4. Enable the input source for the keyboard layout you're testing by selecting the checkbox next to it.
5. Make sure that "Show Input menu in menu bar" is enabled.
6. Choose Show Keyboard Viewer from the Input menu in the menu bar.
7. The Keyboard Viewer showing the keyboard layout appears on your display.
8. Type the key on the keyboard that doesn’t respond and see if the corresponding key highlights on the Keyboard Viewer. If it does, that key is functioning correctly.
9. An apple article is there : If your Apple wireless mouse, keyboard, or trackpad aren't working as expected - Apple Support

Markus_Engelhardt wrote:

After an update to El Capitan the keyboard of my Macbook late 2008 doesn´t work like before: the most keys don`t
show the right letter on screen as typed on keyboard.

If you try to type asdf and you are getting åß∂ƒ, that indicates your machine thinks the option key is always depressed. If an external keyboard works ok, that indicates it is likely the internal one has gotten damaged physically.

Your list contains errors which indicate you are using an OS version much older than El Capitan, or copying from old materials.

1. In system preferences, you select Keyboard (NOT Language and Text)

4. There are NO checkboxes for input sources for a long time now. Instead you use the Plus and Add buttons to add them.

I recommend you update your knowledge about how this part of OS X currently works to avoid posting possibly confusing answers.