Windows 7: Live TV Problem

I've got Windows 7 Pro Media Center working - I'm very impressed but I keep encountering one problem I just cannot sort out on my own.

Sometimes when I goto live tv it goes to a black screen and I'll get some sound occasionally (1 or 2 seconds) then back to black, sometimes I get the program title appear for a couple of seconds before return to black and sometimes I'll get the time bar appear for a few seconds.

When this happens processor usage is 100% (mostly ehshell but also ehrecvr).

I had originally noticed this on occasion on wake up and found a reboot resolved, however, it's now started appearing on boot up too.

All my drivers are up to date as are the Windows updates (checked just now) & I'm at a loss as to what might be the problem. Any advice would be appreciated.

Thanks