When I replaced my brake rotors and lines, I let the system go totally dry and I had brake problems for a while. The VX would stop, but if I kept pushing on the pedal it would eventually go to the floor. After bleeding the brakes multiple times, replacing a leaking hard line and trying just about everything else I ended up replacing the master cylinder and that seemed to solve the problem. My guess is that while the system sat dry for a couple of days the seals in the master cylinder got damaged (maybe dryed out or moisture got into the system). My master cylinder may have been going out to begin with, but sitting dry for a couple of days sure didn't help it out.
I think you've already found out that to bleed the system you need to pull the ABS fuse and have the motor running, but if not try that first.
"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong, it usually turns out to be impossible to get at or repair."
-Douglas Adams, Mostly Harmless