All of the sudden my Jenson has a red lock icon in the upper left corner.The TV was given to me so I do not have any sort of lock code set up.

Contact the authorized service centre. If you wish to get some details; check the site linked here. Pull up older posts. Surf the site with patience. http://electronicshelponline.blogspot.com/
Faults & possible causes to LCD & Plasma screen are given with illustrations. You can get an idea about the fault to an extent.

Blinking rex x on upper left corner of RTI remote

Press the "Menu" button on the remote control and use the arrow buttons to scroll down to the "Parental Guide" option, then press the "Enter" button.
Type in the default parental code "6688" if you have not set your own code. If you have set your own code, type it in. If you set your own code and forgot it, override it by using "6688."
Use the arrow keys to switch the parental lock to "OFF." This allows all programs to be viewed no matter the rating. Press the "Exit" button on the remote and start watching all your channels

Try a few "universal methods" for unlocking the child lock. Some televisions have a universal code built in for disabling the child lock --no matter what your code is. A common code is "0000." or '8888'

Unplug your television for a few minutes. The internal battery of the TV is what helps remember what your code. If the TV is unplugged for an extended period of time, it clears the internal memory, which in turn will reset your child lock code.

If the above does not work try this
the resolution to this issue is to hold the display button down for 3 secs

tienes una mancha en la pantalla tiene que desmagnetizarla o revisar los conectores de la pantalla

Try this: press "Function" and "Mute" on the remote at the same time. This will unlock the channel. Do this if you want to bypass the lock to watch a certain show or channel while leaving the TV locked. All other channels will remain locked and the TV will lock again when it is turned off.
Unlock all of the channels on the TV by entering 0711 or 3308. These are the Jensen factory reset codes that will reset the TV to the original factory settings. By doing this, you will loose any information that you have stored in the TV, such as channel labels and schedules. You will have to program the TV again by going through the entire initial set up.

My Advent TV did the same thing. Blue Screen with a red lock in the upper left corner. Just press and hold the display button for about 10 seconds. It will clearn

The Product: Electrohome 27E510

The Problem:
3rd Party Universal Remote when trying to "scan" for correct codes inadvertently activates a diagnostics setting on the TV set.

The Symptoms:
The word "FACTORY" appears on the upper left quadrant of the screen in RED letters & suddenly all controls are "Locked Out." Television will not respond to button presses on original remote or on it's built-in-buttons on the side panel. All settings/options are "Locked Out" & the TV can only be shut OFF by physically unplugging it. Additionally, when the TV is plugged back in, it is still in the "ON" state & remains in "Locked Out" state.

The Solution: (thanks to a couple of hard-working Support Personnel at NESA)
Plug TV back into power source. Wait until it powers up and the word "FACTORY" is visible on-screen.
Press 6-4-8-3 on the TV's ORIGINAL IR remote device.
You are now in the diagnostic settings Sub-Menu, & the word "ADJUST" will be on the screen.
Press "MENU" on your TV's ORIGINAL IR remote device.
The TV is now back to it's former fully-functioning state.

my tv is locked & the screen is blue . how do you unlock it ?

Hi all you Telefunken TTV-215 owners. My tv did this to. Panasonic in Bloemfontein helped me by phoning Telefunken and getting back to me within 10 minutes. All you have to do is turn your tv on and then press and hold the F button on the remote and while doing this press and hold the MUTE button also. If this doesn't work try olding down the display button on your remote for +- 5 seconds. If still no results try phoning your nearest Panasonic dealer.