How to get "OK Google" to work

Windows 7 64 bit. Using Chrome Browser and Google Search Engine.
I installed all 5 variations of Google Voice Search and enabled each one separately. I can get the Mic icon on the search bar and solid but speaking "OK Google" elicits no response. I can click the Mic icon and it says it is listening, but ask it something and it pretends not to hear me. I checked the microphone and it is working. I ticked the enable OK Google in the Chrome settings. I signed on to both Google and to Chrome.
I find that the voice search is working on my Android Phone and Tablet and also on my W 8.1 netbook.

Thanks for replying "TrashZone",
It seems now that there was two reasons it was not working:-

1. The built-in Mic was faulty in that you could test it and cause the green bar to respond; but it does not pass on its response to associated apps. When I inserted a USB mic it did work. (as a Mic - but still "OK Google" did not work

2. The "OK Google" app/extension was just not working despite a working mic and all the checks I did (including a re-start). However; today its all working fine. So maybe I have an intermittent laptop fault or maybe Google Chrome had a fault for that day.

Yes; there is a built in web-cam (Crystal Eye), but I have never used Skype. Partly because I remember what all my correspondents look like and I get "Free" phone calls to them all on my Talk Talk contract (including Pitcairn Island)