Keurig after filling cup fails to pull water from reservoir
There is a major design defect with all the newer Keurigs, including the B60 and the B70/B77. My understanding is that Keurig has redesigned the pump mechanism that extracts water from the reservoir and into the brewer (there's a second pump that forces the hot water through the K-cup, and it's not involved). They are now using a small DC motor and impeller pump, which is much quieter (to address complaints in many reviews) but the new design just doesn't work.
It appears that air gets into the system, and the new pump isn't strong enough to "self-prime" in this case. So the pump motor runs and runs without water going through it, and eventually turns itself off so it doesn't burn out (it should usually take only a few seconds to fill the internal tank). Many people think the problem centers around the 'check valve' in the base of the unit, just below where the clear reservoir seats itself: Theory is that the tiny pump can't pull hard enough to open the check valve to let water flow, especially when there's any air in the system.
I've had two B77 units already myself, and both have failed this way within only a few weeks. FWIW, the workaround I discovered is to turn the unit on, and lift up the water-filled reservoir about 1-2" as if you're removing it. Then jam it back down into place, hard and fast. Doing this injects just enough pressure into the system to open the check valve, and if the pump motor is running, you'll hear (and see) it immediately start transferring water from the reservoir to the chamber. You'll often have to do this between each cup you brew, and again when you first turn on the system.
There are hundreds of similar reports all over the Internet about this issue, and apparently no real solutions from Keurig yet (I don't even know if they're acknowledging the problem). Other symptoms include brewing half-filled cups of coffee, as others on this forum have reported.
I suggest everyone call Keurig's customer service and file complaints about this until they come up with a fix. Don't let them tell you it's a problem with your AC power or your hard water (they'll try excuses like tthose first). And until they redesign this, there's not much point in having them ship you a refurbished replacement for your brand-new machine, because chances are it will quickly fail just like your old one.