2003 Focus doesn't seem to have much power all of a sudden

check your fuel filter and fuel pump pressure

With the oil light coming on and the brake pedal being hard to press I would say that the engine stopped hence no vacuum -no power assist from the booster.- hard brake pedal. The lock uo feeling may come from the engine seizing up while you were still in gear

Could be a number of things but may want to begin by checking wiring to starter, battery, or even the ignition switch. These components may not turn your engine light on.

Its possible that your catalytic converter is clogged and its not letting you get sufficient power when you press the gas. If its the gear thats now powering enough, there may be a possible problem with the transmission.

Have the radiator checked for blockage and replace the thermostat. If the above doesn't cure the problem you may have a leaking cylinder head gasket

Hello! #1...I need to know if the Check engine Light is on...If it is, take the vehicle to an Auto Zone or Advanced Auto (any auto parts store) and they, for free will read the code/codes...send the trouble codes to me and I'll fix your Focus...#2 tell me which engine is in the car; give me the sub model ie...SE, ZTS....etc...If there isn't a CEL tell me....Guru...Saailer

I’m happy to help further over the phone at https://www.6ya.com/expert/david_6df67de3b14de867

chane the fuel filter, and the air filter. If this doesn't help, Have the fuel injectors professionally cleaned

Since the engine light is not on, I think you have a problem with fuel. Replace fuel filter and test again.

Feel your heater hoses and see if they are getting hot..If so when your click from the switch ,,make sure the door is switching from hot to cold

Check the detachable portion of the "faceplate" on the radio. It's where the memory buttons are. That sometimes doesn't get a good connection and the radio won't work.