Panasonic GT25 Way too dark

if you are using hdmi, check taht the setting under picture mode/hdmi-dvi is set to auto.

aslo try a factury reset

to reset the set, power on the tv,
hold the menu button on the remote and at the same time
hold down the volume minus button on the tv, after about 5 seconds
you will see a screen with information come up,
at this point hold down the power button on the front of
the set until it turns off, then unplug the main power for
30 seconds plug back up and it's like you unboxed it for the
first time.

hmm, the no signal black screen is interesting.
back when the 10' models came out and the discovery of black rise, some wondered if
doing what happened to you, no signal, would help lower black level.
try vivid mode for a while.
crank it up and sharpness too.

one thing more,
in Service menu there is VSUS --- Low.
try setting it High.
good luck

I'm on THX. and my picture looks super beautiful.l
Contrast - 100
Brightness +59
Color + 75
Tint 0
Sharpness +75
Color Temp - Warm 2\
Color Management OFF
CATS OFF
Video NR OFF
Blur Reduction ON
Advanced Picture : Mosquito NR ON and Black Level LIGHT

I did drop the High Green Gain down 2 points on the HEX scale in the service menu. Panasonic emphasises GREEN alog, and their Phosphors on this model had extra green , extra thick green phosphor as well.
If this does not help I can get into my Service Menu and get you all of those settings.
My TV is on up to 24hrs a day with content going all of the time, i have some negligible Magnetic Resonance of USA and other various TV logos but it's barely ever noticeable. I've never seen the phosphors age unevenly on this model /;burn in, just the
magnetic retention/shadowing left from how the black level operates. Real Black Drive uses 2 polarized magnets to keep the plasma state at deep black instead of current. Those magnets can hold a state for a while.
I've gotten rid of it before when i tried, but those channels are on so often it doesn't matter. there's not a hit of phoshpor burn in though.

ITs WAY BETTER than my Toshiba REGZA from 2004 that had very uneven phoshpor wear due to alot of 4:3 content being viewed on it, to the poinit that the side bars were way richer than the center due to phosphor aging mismatch.
My GT25 has seen way more 4:3 wear and tear and there's NOTHING to say about the sidebars at all.

Yeah, service menu is confusing!

I notice there is Cinema mode in the Service menu but not THX. Anyone know if this IS THX? By way of deduction it would seem so.

If you can see VSUS in Cinema then, i'd guess you press whatever button the directions say to select it then press vol up down to change it.
Will look again in a bit. Watching NFL hoping RAVENS can get the job done here on Peyton.

I just saw this, What is your hours?
Don't reset it as I don't know what that does or if you can.

http://www.hometheatershack.com/forums/hdtv-video-displays-processors/23475-how-check-hours-used-your-plasma.html#axzz2HoVKLC7K