My brake pedal will not budge, and a hissing noise present when running

there is no air in a hydraulic system or if there is , the clutch will not disengage
if you have any sound when depressing the clutch pedal, it is most likely from the throw out bearing running dry when pressure is applied to the pressure plate fingers
so it amounts to this
if you press on the clutch pedal and you can readily engage first gear or reverse and you have steady operation when you take your foot of the pedal , the clutch system is working as it should
that means that any noise you get when pressing on the pedal is when the throw out bearing is placed under load and as there is no other part that is moving, that is the logical area
one point here --if it is an air noise and of that you are sure , when people press on the clutch pedal, to stop vehicle movement they also have the foot resting or pressing on the brake and a hissing noise here can be from a vacuum leak at the brake pedal from the brake booster
easy to check before pulling a box that doesn't have a problem

• Knowing the warning signs of impending trouble can go a long way toward keeping your car from a highway breakdown.
  
  You need to develop an awareness of how your car should sound. For instance, when you turn the key to start, the gear like sound of the starter motor engaging should be smooth and sound like an electric motor working hard to crank the engine. If you notice a different sound - more like a grinding - chances are you have a starter motor problem about to happen. Let's say you're driving along and you feel the steering wheel vibrating at certain speeds. The onset of this subtle vibration could tip you off to a tire that needs to be balanced, worn steering linkage or a bulge in a tire that may be about to blow out. In any case, the vibration needs attention. Normally you shouldn't notice the sound of the exhaust system. A sudden change in your car's sound, therefore, isn't something to ignore.
  
  Suppose you're used to a pleasant hum, then, perhaps after a bump or when starting up the car one morning, there's a loud roaring that sound like a hot rod without a muffler. The harder you press the gas pedal. The louder the noise becomes. A noisy exhaust means the exhaust gases are blowing out under the car rather than at the rear of the car - a dangerous condition. Brakes play their own warning tune. On many cars, a scratching noise coming from the wheels that stops when you stop pressing on the brake pedal is caused by a low-brake warning device. Its purpose is to warn you that you need front brake pads. A loud grinding noise when you step on the brake pedal is an alarm that your brakes need immediate attention. The grinding noise occurs when the brake pads are totally worn away and the metal of the brake pad backing plate rubs directly on the brake rotor.
  
  Ignoring grinding brakes can be a costly - or even deadly - error. Shock absorbers help keep the car steady and balanced while the wheels roll over bumps and ruts. Their modern counterpart, the MacPherson strut, does essentially the same thing. You might not notice worn shocks or struts when you're simply riding around town. The safety effect of these devices comes into play at higher speeds. When you hit a bump, the tire wants to bounce like a basketball. Worn shocks or struts allow the ties to bounce out of control making steering difficult and braking less effective.
  
  What you may notice is the car rocking more every time you stop, assuming an almost boat like quality. Old, broken or worn out shocks and struts should be replaced to ensure safe steering and braking at higher speeds. Engine noises are easiest to hear when the car is not moving. Transmission sounds or brake noises usually occur when the car is moving. Pay attention to any new sound and keep notes - how it sounds, when it makes the sound and what difference, if any, occurs in driving when the noise is present - to help you describe it to your service dealer.

you don't say where the noise is. that is important to give a clue where the issue is. when stopping on the brakes 3 things happen. you press the pedal and the abs pump starts pumping fluid. the second is the brake capilers start pushing on the rotors to slow the car. the rotors are attached to the wheels and that stops the car. so if the rotors are warped you will feel a vibration in the steering wheel when stepping on the brakes. if its your foot feeling the pump working that is normal for abs pumping. you should feel it and holding the pedal will keep it working and stop you from skidding if everything is working correctly

yes but up to a point
the brake pedal should move about 1" to take up the pedal free play and then be applied smoothly as you press further
the harder you press the more solid stopping action you will get
that way you can feel the brakes working so that you can adjust the braking action for stopping
there should be no hissing noise that occurs when the brakes are being applied
you say hydro booster which is hydraulic booster but a hissing noise will come from an air leak in a vacuum brake booster which indicates that it needs repalcing

hissing noise is a leaking diaphram inside power brake booster.you have to replace the power brake booster.

Hi Shelly, Your explanation is a little short on detail. I suggest that you take a length of plastic tubing and while the engine is running, and the hissing sound is evident, place one side of the tube to your ear move the other end to the different units fitted under the dash until the noise is loudest. Once you've done that you can identify where the defective joint or unit is. Regards John

The air seeping is a dead giveaway. Your power brakes are now manual brakes, but stiffer. The diaphram in the brake booster has torn and the hissing noise is the engine vacuum escaping (you hear it louder when you depress the pedal right?). Replace the booster and you will be fine. The brake lights probably don't work because you can't push the pedal down far enought to release the switch. Please rate. Thanks.

Is there any problems with the brakes besides the noise? If theyre acting up, it could be your brake booster. It's hard to determine without more specific details, brakes always make a quiet hissing noise, depends on where, how loud, how the pedal feels...

most likely have a bad diaphram in the brake booster that hisssing sound is vacuum leaking under hood there will be hose going to brake booster unhook hose and pinch off hose start car does hissing sound disappear if so bad booster

you mean you hear air in the cab down by the pedal. If thats the case your power steering assist is leaking. Its the big black unit behind the brake master cylinder. It may set a check engine light at times for lean condition.