I sort of wonder if the initial symptom, of the HDMI signal quitting and the display freezing (but no red lines?) indicates a shorted decoupling cap on a digital board somewhere. Or failed unobtanium IC.
But concur with the comment that pulling the main regulated output of a cheap multi rail SMPS could cause the other rails to run high. But, I've not personally seen VFD filaments run direct from the main SMPS. More usually from an onboard inverter that also provides the -25(ish) voltage. But, there again, I rarely work on "consumer" stuff.
You may find, when disconnecting the PSU from the rest of it, that the main rail (+5 or +3.3) is fine, but the others are now low. That would indicate the PSU may be OK. (Check by loading the main rail to something like half an Amp, and see if the others come back, so long as that main rail doesn't collapse under any load, however small, in that case the PSU is likely duff.
SMD Tant' caps are prone to suddenly going short cct, especially those placed across a power rail. (Don't ask how I know..) They don't tolerate surges too well either.
Even if you can't fix it, you'll learn a load about fault finding, that will do you well in the future.
Good luck.
Dave 'kbv.