TV was Fine last night, this morning there is picture, but no sound

I have a Philips TV that is about 4 years old. Everything was fine with it last night. Today, I was cleaning and used the vaccum dusting attachment to clean the back of the tv (it was not turned on) and behind the entertainment center. After I was finished cleaning, when I turned the tv on, there was a picture, but no sound at all. The only difference that I noticed, besides the silence, is that "mono" shows on the screen everytime I change the channel. The closed captions work and I was reading in another person's post that that could mean that mute is on somehow. I muted and unmuted with the remote, but nothing changed. I plugged headphones into the headphone jack and could hear background static-y noise but no true sound. I tried playing a DVD to see if I could for some reason get sound like that, but when I put it on the channel for the DVD player, all I get is a black screen instead of the menu screen coming up. Any advice or suggestions you can give to help locate and fix this problem will be greatly appreciated. Thanks.