I own a Avermedia as well. (AVerTV Hybrid Super 007)
(M135 chip)
I had the same problem in Windows XP was able to resolve but don't remember how....
And now i have that problem again with my new pc and windows 7 (64bit).
I was able to resolve it, by actually uninstaling the Avermedia software and then let the device manager re-recognize the card without reinstaling the software.
After that it works fine on Windows Media Center. No more grey image.
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My issue tough (and why i am still not with a solution)... Is that Windows Media Center despite being a very nice software, has a huge huge huge huge failure. It lacks to assume that your TV card has other inputs.
I know of the workaround "solution" is saying you have a set-top box. Frustration there is seing it making a preview of the other input (where my Nintendo Wii is connected) and me seeing it and hearing it, but being unable to conclude the setup just because Media Center is not able to detect the set-top box IR hardware (I even went as far as to buy a windows media center USB IR receiver with remote control, thinking it would resolve my problem, but it did not... says the same message despite me using the remote without problems inside the Media Center)
I try using the Chris TV. Because it lets you add S-Video as one of your channels.... But when i do that, all becomes grey image again... (argh).