I second the suggestion to re-run the TV setup. Sometimes the guide providers change headend IDs, which will cause guide downloads to fail or return no data.
I was suggesting Big Screen EPG just for the reset, I wouldn't recommend it for the Canadian/US listings. It's possible to do it, but way easier to just run the hack.
I may have been making assumptions here that you're using Windows 7. What version of Windows and of Media Center are you using?
The reset I think only works with Vista TVPack or Windows 7.
I did some searching, and came across a thread where some others are having the media player connection error. Seems like in their case it was an nvidia driver issue. http://thegreenbutton.com/forums/t/83722.aspx
My next recommendation would be to install SP1 for Windows 7 if you haven't already, that will refresh many of the media center files in case any of the executables have gone bad.
Last but not least, a full reinstall of Windows 7 should cover it if you have the media and/or restore information from HP.
If it doesn't work as configured by HP, with additional updates from Windows Update, then you might want to invoke HP Support as well. The first level will be painful, but they will have ability to escalate to Microsoft.
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