No air will come out of my vents, only the ones near the window for defrost. What's blocking the flow?

I have checked the vent openings and do not see anything blocking them. I am a 62-year-old woman and was hoping to get some help before I have to resort to going to a garage. Would appreciate any suggestions. Only heater works for defrost. Air conditioning is not working at all, which is why I bought the Freon. I do not want to use that yet until I figure out why the vents are blocked. Thanks for any help!