One of the vents in my room is not blowing hot air, when all others in my house are working fine. No air is blowing out of this vent. What would be the cause of it?

Are you sure it's a supply and not a return grill? Is there an adjustment lever? If it is a supply, there could be a duct damper that is closed. If the ductwork is spiral fiberglass, the duct could have collapsed or the inside could have come loose.

Thanks ma0641. Yes, it has the adj lever to open and close. I've been asking around and many people are saying it could be due to duct disconnect. I guess I have to make a advanturous trip to my dark attic..

I should have thought of that too. Look for rodent damage, I've fixed a number of them where squirrels have chewed them open. Not sure what is appetizing. Be careful and don't fall through, Brian