If the blower motor fails to operate following engine start, try turning the ignition key slightly to the left. Should the blower motor suddenly engage (and you can repeat this effect) then your ignition switch requires renewal (# 202 545 01 04; approx $22.00)
If the motor fails to operate, remove the right lower dash access panel (3 chrome screws and two grey plastic clamps) and firmly rap on the blower motor housing. If the motor starts, then the brushes are likely worn. Remove the motor (4-5 screws?) and inspect. If only the brushes are worn then consider renewing them (replacement brushes are available from aftermarket sources). If anything else is worn/damaged, then consider renewing the motor.