Q: Brake pads fixed, parking brake, car won't start.

If the parking brake warning light is on and yet the parking brake is disengaged, that typically means that the switch is stuck. If the warning light yo are seeing though relates to the brakes generally, that could mean the fluid level in the master cylinder is low (low fluid level warning light). The brake system is unrelated to and separate from the "engine". Even if you took all the brakes off the car, the engine would still start. Consequently, the no start problem you are having arises as pure coincidence unless somehow the mechanic worked on parts of the car other than the brake system, such as the engine.

A possibility is you have a weak battery. Consider that a strong possibility if your battery is 4 years old or older. Prior to performing diagnostics be sure you have a fully charged battery that passes a load test. Then, confirm that the engine immobilizer system (security system) is not activated thus preventing the car from starting. To temporarily override the immobilizer system, see these instructions. With a fully charged battery and the immobilizer system off, if the starter motor does not operate at that point, either there is no power to the starter motor, hence the starter circuit would have to be diagnosed, or the starter itself is bad and it would be replaced. On the other hand, if you do have a fully charged battery that is powering a starter motor that is turning the engine over rapidly, at sufficient RPM, but the engine does not catch and run, that means that there is an ignition, fuel, air induction, or mechanical fault in the engine that will have to be repaired. Be sure there is adequate fuel in the fuel tank and that the fuel is not old. Check for adequate fuel pressure (does the in-tank fuel pump whirr momentarily at the instant you turn the key to the "on" position?; if not, you have a dead fuel pump), injector operation, and a spark at the spark plugs. If the simple checks I have outlined above do not result in the car starting the recommended service to request is a no start diagnostic during which the responding certified mechanic will get this resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.