* Brake Booster Failure: The brake booster uses engine vacuum to assist in braking. If it fails, the brake pedal becomes incredibly hard to press, requiring significant force. A failed booster can also cause the brake light to illuminate (as it indicates a problem in the braking system). While the booster itself might not directly prevent the engine from starting, a related vacuum leak could disrupt the engine's operation enough to cause a no-start condition.
* Master Cylinder Failure: The master cylinder is the heart of your braking system. If it fails internally (such as a seal rupture), it can lead to a hard brake pedal and brake light illumination. This failure *could* also affect the vacuum assist system and indirectly prevent engine starting, or in some cases, damage components connected to the vacuum line.
* Low Brake Fluid: While less likely to cause the hard pedal *immediately* (it often leads to a spongy pedal first), critically low brake fluid can indicate a leak somewhere in the system, causing the hard pedal and brake light. This, however, usually wouldn't directly stop the engine.
* Vacuum Leak: A large vacuum leak in the engine's intake system can affect the brake booster (hard pedal) and prevent proper engine operation (no start). The brake light might be on due to the brake booster failure or low vacuum triggering a warning.
* Electrical Problem: While less probable given the brake symptoms, a serious electrical fault *could* simultaneously impact the braking system (causing the hard pedal and light) and prevent the engine from starting by disabling the starter motor, ignition system, or fuel pump.
What NOT to do:
* Don't attempt to drive the car. With a hard brake pedal and a no-start condition, the vehicle is unsafe to operate.
What you SHOULD do:
* Call a tow truck or roadside assistance. This is not a problem you should attempt to diagnose or fix yourself.
* Do NOT attempt to "bleed the brakes". This is only a solution to a problem related to air in the brake lines, and this is likely a much more serious problem.
This situation requires professional diagnosis. A mechanic will need to inspect the brake system, check for vacuum leaks, and investigate the electrical system to determine the root cause of this multifaceted failure. Ignoring this could lead to serious safety hazards.
