When the buttons quit working, does the green light on the controller stay on? Check and see that the buttons still work in Windows. To do this try the following:
(I am on Windows 7) Open Control Panel - Devices and Printers. Find the Controller. right click and select Game Controller Settings. Choose properties. You should see a window that allows you to calibrate the controller and to press the buttons to see if they work. Do they work? The Mach plugin does not shut the buttons down. It does include an option to lock the controller so that nothing works until you unlock it.
If the buttons do not work in the Windows Devices calibration screen then my guess is that the problem is related to a power saving setting either in the BIOS or in the Windows driver. The other thing is that it could be the USB port that you have it pugged into. Try a different USB port. The other possibility is that the Controller is defective, but I doubt it.
Hope this helps.