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

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?