I have an old (may be 10 yr) all electric central AC. Recently blower quit working intermittently. Can you help me diagonose the problem?

Symptoms-
Outside line become frozen. No air is blowing inside.

Action required to get to working:
Let the outside line defrost. Changed the capacitor (recently). As soon as I turn on the fan makes noise but it does not move. Turn of the power switch. Manually spin the fan (just a push like you would be doing to get started manual shift car!) and turn on the power switch. All works for few days/weeks until the symptoms come back again.

I am not a tech or engg and I can only do the simple stuff like the one described avobe.

Can someone tell me what's wrong with the AC/Fan? Why do I have to push start the Fan?