Motor bearings seizing up? If about 20 years old and used for both heat & Air Conditioning, it is likely time to replace the blower motor. Mine did the exact same thing to me this summer (22 years old) capacitor worked for a day or two, then stopped. New motor worked ever since.
Repair Clinic.com (Canton, MI) has bunches of them in stock if you want to make the short drive up today.

Repairclinic.com is open until 7pm for counter service.
Order online by 6pm and it will be waiting for you. But, if you don't preorder and get there at 6:55 and there are people in front of you, they will wait on you no matter how long it takes.
Best to preorder to verify they have yours in stock. They also have universal models.
800-269-2609 if you want to call in an order.

There may be a small hose attached to the shroud surrounding the "squirrel cage" of the fan assembly. That hose would connect to a sealed bladder assembly that gets pulled by the suction created by the spinning squirrel cage. There is a micro switch on this bladder that signals if there is a suction created by the spinning fan/blower. If it doesn't spin, there is no vacuum and the switch does not activate so the furnace shuts down and a fault code is generated.