e30 brakes not working

[sadham]

E30 M10 318I,
I had recently (long time ago, but never actually driven the car since)
Bled the brakes as I put new (rebuilt) front calipers on both sides.
Put the pedal box back in.

The brakes feel stiff when car is idling but when I start driving the pedal goes straight to the floor and barely even works.
I can hear a hissing sound when pressing them, the fluid isn't going down.

What could the problem be?

[Brianmoooore]

Hissing noise is from the servo, and is normal.
First thing I'd do is thoroughly bleed the brakes, preferably with a pressure bleeder.