We have seen a rash of issues with gamepads all of a sudden running windows 8 and version 40.0.2214.94 of the Chrome browser. In our experience, upgrading to the latest version fixed the issue. Note, the upgrade happens automatically for most people and so this may be a non-issue after a week or so.
In our case we were using a logitech F310 gamepad. On the PC it is supposed to be in ‘X’ mode (the switch is on the back). Even so, the A/B/X/Y buttons did not respond at all. Neither did the D pad.
Checking your google version number: