Help Audio And Sound On Computer Not Working?

I just dowloaded avast antivirus, zone alarm and a new spyware system yesterday, but when i was using youtube this morning, it was working. Now several hours later...theres no sound coming out of my speakers =(
i tired earphones but they didn't work. Is this because of what i dowloaded yesterday? Is there soemthing that needs to be replaced? PLEASE HELP!!!