Clutch goes to floor without engaging - 1988 Honda Prelude

A clutch pedal normally does go all the way to the floor. If you can shift gear without a crunch, it is disengaging OK.

The loss of power could mean the clutch plate is worn and is slipping when engaged. There is a crude test for this. Start the engine and idle it. Apply the footbrake firmly, depress the clutch and put the gearbox in 3rd. Let the clutch out slowly. If the engine does not immediately stall, the clutch needs replacing.
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You have leak in the system, either the master cylinder, the slave cylinder, or the line itself.

Once the component that is leaking is found, it needs to be replaced or rebuilt, the system filled and bled to get the air out.

engaging?
you meant dis-engage im sure.
pedal up is engaged,
pedal at floor dis-engages it.
my guess, is the clutch drags unless i push the clutch pedal 100%
to the floor.
1: bad cable is 90% cause. non last this long.
2: no free play is way too loose.
3: broken lever on the pedal top. caused by #1

all fail modes covered here.
http://www.fixkick.com/tranny/clutch/clutch-on-kick.html

If your fluid was low (which is why you likely added some,) you may need to "bleed" your clutch master cylinder.

You will have to be more specific in order to get help on this site .... does the clutch go to the floor randomly without pushing it with your foot? Does it just go to the floor when you press it with your foot? If the last is yes then does the transmission disengage when the clutch goes to the floor as it should or does something else happen? Normally you would want your clutch to go to the floor ... see where I'm going with this?

Your car has a hydraulic clutch release system, it is defective, either the master or slave cylinder is leaking or pulling in air and this causes the clutch pedal to go to the floor.

I don't know that specific vehicle, but if its a hydraulic clutch it sounds like either you have a leak and your clutch fluid is low, or the master or slave cylinder could be bypassing internally. Check the fluid level in your clutch master cylinder. If its low, you should top it off with brake fluid and will probably have to bleed the system. Also look for leaks. You can probably find info or a video online of how to bleed the system. Its a bit hard to explain without illustrations or pictures. Not really very difficult to perform. Good luck.

Try to adjust the clutch to compensate. if the adjustments have already been made and, the pedal is very close to the floor while engaging. this will confirm pressure plate failure.

replace the pressure plate in this case.

I found that having a wood stick on the clutch pedal down to the floor all night (the other end of the stick held by the seat. oh yeah !!! ) would help to ease shifting for the first hour the next morning, then it would come back stiff and hard to engage in gear.

The trick to driving a manual transmission is giving gas very gently while letting the clutch up. The clutch only starts to engage when the pedal is about an inch and a half from the floor, so any gas you give before that will cause unecessary revving.
To get a feel for when the clutch engages, try the following excercise. Put the car in first gear and bring the clutch up ever so slowly without giving gas. At a certain point you will feel the clutch starting to engage and hear a difference in the sound of the engine. If you're bringing the clutch up too fast the car will stall. If you bring it up slowly enough the clutc will start to engage and you will begin to advance.
This excercise will develop your motor skill to manipulate the clutch effectively and will allow you to know exactly when to give gas when letting the clutch up.