I think a few inflatables had been packed slightly damp last xmas. While most work a few dont. I took off the housing and when connected they do hum and will start but only if I give the fan a manual spin ... any ideas

 

If the bearings have suffered from any rusting then certainly, at the very least, they need lubrication. If the motor is lubricated and allowed to run at speed for a while, that should free it enough so that it can start on it's own. Worst case it may need to be taken apart and the bearings cleaned and lubricated.