My computer was recently left on for an hour and i went outside to go biking. When i came home, i went on youtube browsing videos, and i found out that no sound was being emitted from my computer! I checked my speakers and they were all plugged in and fine! Then i noticed that even though there was supposed to be sound (meaning that the windows 7 sound thing should show the sound level of what's being played) doesn't show any sign of sound being transferred. I also went to control panel to test some sounds for my speakers, and when i clicked test, it said "Failed to play test tone." What's the problem here?