If the breaker which powered the outlet had tripped, wouldn't it take the TV with it as well? does the TV turn on? if so the outlet is ok. now if it had a GFCI right next to the outlet the tv was plugged into (odd but it has been done) and the GFCI tripped, the converter would obviously have zero power and the tv would. but this isn't the OP's problem.
The OP had the box suddenly turn off. sounds a lot like power down. none of the boxes i've used, have even given a warning box that it was turning off. if you haven't pressed any buttons on the box's remote or changed channels (some people like watching one channel during the interval of the power down, some boxes have it pre-set at 1 hour, some 3, some 4) the box would have seemed to go off like a light. or the OP tried to turn on the TV to sit down for some DTV viewing and found snow and no LED lit on the box itself.
it could have gone 'bad' but again my experience was the box acts like **** when it goes bad, it doesn't go from a working condition to a dead set instantly. for that to happen it would have to be really crappy quality or it was used during a storm.
now if the OP has a GFCI outlet nearby i'd at least try the box on another outlet in another room (why is because you'd be surprised how many GFCI outlets control the outlets in another room or even half a house for no reason; the one in my home is in the bathroom and if it trips the living room AC outlets and DC lights fail to function) not attached to the TV to see if any signs of life come from the box (LED lights up) if so either the GFCI is faulty or has tripped or the outlet in question has no power due to either a tripped breaker (would take the TV with it as well and probably any other outlet on that bus) or a faulty outlet that could pose a fire hazard and needs replacement from a qualified electrician.
Some GFCI outlets have only one outlet protected by the breaker integrated into it. again, don't ask why i've just noticed that when those kind go one outlet works when the other one doesn't. does this outlet have reset buttons or a test/reset button? if the answer is yes, does pushing the 'test' button make it click? if the answer is yes, try hitting reset and test the outlet with a lamp. does the lamp work? if yes the outlet is working and the next step would be to go to the box itself. if the answer to the test button is no, try hitting reset and see again if the outlet works. if that answer is no, or the reset button continues to immediately pop out, the outlet is faulty and requires replacement.
As in my case, the outlet with GFCI buttons can even exist and have nothing plugged into it in an entirely different room (bathroom and kitchen and in some cases, garages) and any one of them could have tripped even without load, and for some reason (ask an architect why because i do not know) they're wired in series to a room next to the offending outlet or even part of the home is wired to it in series, so when the outlet trips for whatever reason, anything in series with that outlet, be it the lights, microwave, TV, or converter box, go out with it.
Is it plugged into a surge strip? what is the condition of the surge strip and what else is plugged into it? some surge protectors have a red light indicating if there is power and also a 'Site Wiring Fault' light on the more recent ones, and a built in circuit breaker. also this breaker could have tripped and took out the surge strip. some surge strip disable the protected outlets (but not the 'non surge-protected ones, common on some Uninterruptible Power Supplies but you never know) if the 'Site Wiring Fault' lamp is lit, even if power is available. that normally means either the Neutral leg is gone and it's using ground instead, or vice versa. and that too can cause the box to fail.
Some converters, the Magnavox included, have a 'master off/on' toggle switch on the side or in rear. if this button has somehow been turned to OFF or '0', either in a fall or from being bumped (by a pet such as a cat or other reason, such as moving around stuff in proximity of the box) the box will also show no signs of life, not even a standby light.