No pressure in the brakes

You have a abs problem. Most likely a wheel speed sensor. Have system scanned for codes. The reason the pedal pushing back is system detected a skid. Brakes should work fine though

neither is bad. The proportioning valve is kicked and they can sometimes be a bear to re center. Here's the best way I've had success doing that. Before you try opening up any more bleeder screws you, 1)top off the brake fluid reservoir, 2) slowly pump the brake pedal, not all the way to the floor and without the engine running but with the key on, about 20 to 30 times. After you do that you very quickly hit the brake pedal very hard but not all the way to the floor. The repeated slow pumping of the pedal will very slowly put pressure into the line, even if it's air it will compress a little at a time and when you jab the pedal that one time at the end it will re-center the valve. Now here's the key. If the brake light is on it should shut off when that valve centers itself. That's when you must bleed the air out but whoever you have helping you tell them not to push the pedal all the way to the floor again or the valve will pop again. Open the bleeder to the caliper that had the blown line and then have them push slowly down on the pedal only half way to the floor and then stop pushing and hold position til you tighten the bleed screw. After you close the bleeder screw they can let up and do it again. If he pushes it to the floor and you hear a click that means the valve kicked again and you need to start over. Time consuming, yes but it works. I hope this makes sense. Sometimes it's hard to relay what I do to words on paper,.
Dale

There is no reset on them. What will work sometimes is to completely remove the brake light switch assembly from the valve and slowly push and release your brake pedal a few times. Then reinsert your brake light switch. If this doesn't work you will have to replace the proportioning valve. New price will likely scare you so head for the scrapyard.

Booster problems are rare but they do go bad sometimes.
A bad booster generally causes the brake pedal to feel hard to push down, and a lot of pressure on the brake pedal is required to make the car stop.
Rarely, a vacuum brake booster will develop a vacuum leak, which can cause engine performance problems, hissing or whistling noise, as well as requiring increased pressure on the brake pedal to stop.

The first test:
With the vehicle parked, turned OFF, and the parking brake set, pump the brake pedal 5 to 6 times. If the pedal gets harder to push after several times, your booster is probably good.

The second test (To make sure):
After the test above, without making any changes, press and hold the brake pedal with light to moderate pressure.
Now with your foot still on the brake pedal, start the vehicle.
If the booster is good, you will feel the pedal go down when the engine starts.

Hope this helps!

air brakes? need to let air pressure reach maximum..then step on the brake pedal and push release in.. wait for air to escape.. release pedal.. if it wont move then spring brakes are frozen.. may need some alcohol added to air to unfreeze brakes if below zero outside..may need to do this a few times..also try to rock the vehicle with it in revese or drive..sometimes the pads rust to the drums..

Did you replace the lines when doing all the work, the lines are the cheapest part of it all

If you are saying that some times the brakes work when you step on them , and sometime they don't , The only thing that would cause that would be worn seals inside the brake master cylinder.
It would need to be replaced.

most common problems will lies in the master cyclinder become faulty. If the pressure feel spoongy or when you press the pedle all the way to the floor and no brakes or with little brakes, it will be your master cyclinder unit; sometime if you have to pump the brake couple of time to get the brake to work. replace the master cyclinder, fairly cheap. if you do it your self make sure you bleed it properly.

You need to bleed the brake lines.....I can tell you how if need be.

The problem is in the master cylinder. The MC is in effect two cylinders in one, one cylinder for the front brakes and one for the rear (one in front of the other). When the MC gets a bit long in the tooth pressure from one cylinder can leak past it's seal into the other cylinder or into the reseviour. The MC is leaking internally, but not externally, so you see no signs of leakage and don't lose any fluid as leaked fluid ends up back in the reseviour. Sometimes the symptom will be evident and other times not, on my car the pedal tends to sink sometimes on hot days but is always firm on cooler days(?). It really is something that does need to be addressed urgently as a matter of safety, because pressure is leaking from one cylinder the pressure in that cylinder won't be high enough. This will affect front to rear brake bias which can have a substantial adverse affect on braking performance, and may cause premature brake lock up at either the front or rear (not sure which end), which could cause loss of control (i.e. massive understeer or oversteer under brakes). $700 does sound at least a bit steep to supply and fit a new MC, and bleed the brakes. Here in Australia new Accord MCs are around AUD$180 or so. The pedal should be quite firm with little free play with a braking system in good condition, if yours typically isn't (before you had that sinking feeling) then the brakes probably need attention (bleeding most likely, but could also be a soft rubber hose, causing the hose to bulge under pressure, not good as it may burst).