Windows 7: Video stuttering on Windows 7 Media Center only

I'm not sure what happened. I have been using my HTPC to watch cable TV using a SiliconDust HD Homerun Prime for the past 2 months without any problem.

However this week, I have noticed that the TV video stutters with pixelation every couple of seconds on all channels, both SD and HD channels. The audio is unaffected. This occurs only when viewing TV using Windows Media Center. Watching TV on Windows Media Player on the same computer doesn't cause any video problems. Meanwhile, I don't have any problems watching TV using Windows Media Center on another computer. In addition the same stuttering occurs when I play a HTPC recorded TV show (on either the SSD drive or WD Caviar drive) with Windows Media Center, but the stuttering doesn't occur when the same show/file is played with Windows Media Player or Arcsoft TMT5.
I don't think this is hardware related because I can load and watch all
DVD and bluray movies on my HTPC using Windows Media Player or Arcsoft TMT5 without any problems, After playing with the video settings, I can watch TV on Windows Media Center without any video problem when the resolution is dropped from the usual 1080p to 720p and after I change from full screen to a window playback.
To my knowledge, I didn't add any new software or change any settings with the exception of the periodic Windows 7 software update. Taskmanager and Resource Manager list the % CPU usage when watching TV at 10-15% with only 40-45% used physical memory. The only unusual measurement I encountered was a high CPU temp of 50-55 degrees. However, I still have the same problem when I turn off the computer, remove the case cover to allow the computer to cool, and immediately start to watch TV when the CPU temperature is very low.

Any help or suggestions that you can give is much appreciated, since I don't where to go next.

Thanks,
Oliver

My HTPC components are
CPU: Intel Corei3-530 Clarksdale 2.93 GHz
Graphics: Integrated Intel GPU
Motherboard: Intel DH57JG mini-ITX.
RAM: 4 GB.
Hard drive: Intel SSD boot drive and 1 TB Western Digital Caviar Green (for TV recordings).