Window icon on taskbar not working

Hi - I'm running Windows 8 and for the last day or so, the windows icon, bottom left of the taskbar, is not working - it is there, but white - I'm sure it was yellow or so before, and it doesn't work. My windows key is working fine, but I've gotten used to the icon - especially if getting out of, say, a game and wanting to go back to the main screen. Also the right hand top hot key is also not working. What do I have to do to get these back again? I've tried cleaning the registry etc, - would it help to do a system restore?
Thanks

Later......Actually it seems to have sorted itself....after trying lots of things, I was doing an update, and got a message that there was a problem, and it was shutting down and rebooting. Anyhoooooo it seems to be working again. Now I know - if it happens again, I'll switch off and reboot! Wish I'd thought of that before.....

If it happens again, do a screen capture and post it here.

Thanks Rich - as you can see - after I re-booted a while later it corrected itself! Now I know what to do... but I wonder why it did that.