Fan on all the time means there is a fault with the fan temperature control switch. When that circuit is open, the fans stay on until the ignition is turned off. The switch is screwed into the lower part of the radiator near the middle facing the engine bay. Check that the connector wasn't knocked loose or disconnected, then check the wires for fraying or corrosion, and finally trace them back to a ground and check to make sure it is sound with no rust or corrosion.
If the engine is running poorly, pull the plugs and see if they are wet from coolant or fuel or fouled with oil. Fuel means a spark plug isn't firing properly or injector is stuck open. Coolant means a head gasket leak. And oil means leaking valve stem seals. Finally check the coolant for an oily sheen and remove the oil fill cap and look underneath it for a chocolate milk-looking deposit, which is also a sign of oil and coolant mixing. Could be from bad head gasket, cracked block, or from a failing oil cooler in the radiator.
Hope this helps!