One among the most likely causes of no brakes is loss of fluid pressure in the vehicle brake system. The brakes works using hydraulic pressure, this is likely to happen if there is a fluid leak in a brake line, hose, wheel cylinder or caliper, where there may not be enough fluid pressure in the lines to jam the brakes.
In some cars, when there is a serious leak, the red brake light comes on when then brakes are applied. This is a warning that there has been a loss of pressure in part of your brake system. To start, check the fluid level in the master cylinder reservoir. If the reservoir is very low or dry, there is a serious brake fluid leakage. Inspect the entire brake system for leaks so that the fluid leak can be traced the fixed.
Sudden fluid loss can happen if a rubber brake hose is cracked or broken, or if there is a steel brake line rusts. This kind of situation is common on older cars that are exposed to lots of road salt and water. Salt is always very corrosive, especially if the anti-corrosion coating on the steel brake lines is thin or of worn out. Once the corrosion eats through the line, there is likely to be a brake line failure as the fluid blows out, you lose your brakes.
If the brake pedal sinks to the floor when you apply the brakes, another cause could be severely worn brake linings and or air in your brake lines, which would need bleeding the lines to get rid of it.
Yet another possible cause of brake failure could be a faulty ABS modulator that is leaking brake pressure internally and has not been sending pressure to the brakes when the pedal is stepped on. Dirt or corrosion in the brake system can enter the modulator and hamper the spring-loaded accumulator valve from closing, making the modular to have an internal leak.
Another situation could be a bad master cylinder. If any of the piston seals inside the master cylinder are worn or bad and are not supplying pressure when there is a push on the brake pedal.
A bad power brake booster that is not giving much if any power assisted braking will increase pedal effort, but it will not cause the brakes to fail. You may have to push on the pedal much harder than normal to stop your car.
Still yet, brake fade and brake fluid boil are other conditions that may happen as a result of the brakes being too hot often because of driving aggressively, racing or riding the brakes for a long time. As this heat builds up in the brake linings, it requires much more pressure to achieve friction and braking force when the brakes are applied. The brake pedal may be somewhat stiff but the brakes do not seem to have any or much stopping power when you apply them. The solution to this kind of brake problem is to slow down and give the brakes sometime to cool. Hot brakes may also make the fluid inside the front calipers to boil. This creates a steam pocket that may increase pedal travel to the point where there is not sufficient pedal travel to apply the brakes. Pumping the brakes in this situation may help.