Tonight, had the same problem where the FBV display got stuck at initialization with "FBV 5B MKII" displayed on the screen. The issue was a faulty (or perhaps dirty) ethernet cable.
Here's more specifics as to the problem. When I start up my POD HD Desktop with the FBV Shortboard MKII connected, the FBV typically shows "FBV 5B MKII" for a couple of seconds before becoming functional. Tonight, it got stuck at that point ... the screen just showed "FBV 5B MKII" and none of the LEDs on the buttons lit up. After playing for a minute, I figured out that the buttons still turned effects on and off (I don't used them in bank up/down mode), but the tap/tuner button would not start the tuner (I could still turn the tuner on by hand using the HD Desktop button). So I was able to limp along through our set as I only needed to turn one effect on and off for the entire night. I switched ethernet cables before the set, and of course, left the old one at home. Our sound man had an extra cable, but I tried his and had the same issue. The FBV still displayed "FBV 5B MKII" and the LEDs did not light up.
After I got home, I tried two additional ethernet cables ... one that is dedicated to using the POD at my computer and the old one I used live up to this afternoon. Both worked with no problems. Using either of those two cables, my FBV initialized just fine (i.e., the "FBV 5B MKII" only stayed on the screen a couple of seconds and then the FBV started working like normal). I'm wondering from what was posted above if the other two cables are just dirty or if they're broken. Seems odd that two cables worked and two did not. I'd have expected only one bad out of four. I may post again if I can figure out what is different with the two cables that did not work.
So bottom line is make sure your ethernet cable is good. And try a few just in case you have the same problem I had.