I bought a new Hewlett-Packard PC running Windows 7 about six months ago. For the first month or two, I could get the sound on YouTube and .wmv files. Now I can't; these files are silent. The speaker works; I have the "system sounds" (beeps, chirps etc.) and get the sound on some moving-picture files. What I suspect is that a software program that came with the computer was a "trial version" that expired after a certain period of time and the vendor is waiting for me to pay for a renewal. I have no clue what that software, or who the vendor, might be. Any useful suggestions as to how I can restore full sound, or acquire the necessary software, will be appreciated.