Hey, registered just so I could reply

I have the same model as you, The service menu trick by Markross didn't work for me either, I've tried many times thinking it was me. However there is still hope as I changed my model from C6500 to C8000 using a tool found via the SamyGo forums, If your not aware that site is aimed at rooting your Plasma.
This tool
does not require a rooted TV and simply acts as a network TV remote but enables you to trigger the extended service menu and access all the extra options. I can confirm this as I've done it myself a few times to make sure it saves, and the only noticeable improvements I can tell are the animated / improved menus.
Anyway the tool is called "ruSamsungTVCommunicator", the only downside is that its in a language other than English, but after a looking through various forum posts I managed to find a step by step guide on how to activate the extended menu.
Either Google it or go to
http://www.rainerullrich.de/samsung/ to download. Below are instructions on how I used this tool with my TV, but as with any service menu tinkering use at your own discretion as it could have undesired effects if miss-used.
*TV and PC must be on throughout this process, so start by turning them on before you begin.
1) Turn the TV and PC
Steps performed on PC
2) Run ruSamsungTVCommunicator.exe
When the program is run for the first time it updates a lot, I dont know what it says but you will be presented by a series of confimation buttons eventually, follow this order to get to the remote.
- Steps on PC
- Yes
- OK
- OK
- Yes
- Auswahlen / Weiter
- Steps on TV (Use actual TV remote)
- Ok to Call message (might not show on all sets)
- Allow New remote
- Tool should now be loaded, continue with steps.
Now the ruSamsungTVCommunicator is ready for use with the TV.
Steps performed on TV
3) Hit MUTE 1 1 9 ENTER
4) A menu will appear that says Hotel mode OFF
5) Click on the RIGHT ARROW on the remote twice, to set HOTEL MODE = ON
6) Turn the TV OFF
7) Hit INFO MENU MUTE POWER to turn the tv on and load the service menu
*If ruSamsungTVCommunicator was already on during the TV reset, it should have displayed an error message, just saying it lost connection to the TV. Simply exit the tool and re-open while the TV is in the service menu. Because we already setup the tool prior to enabling the service menu the tool should load straight into the remote section with no prompts.
8) In ruSamsungTVCommunicator click Factory (TV screen changes colour repeatedly until next step is done).
9) In ruSamsungTVCommunicator click 3Speed (TV screen re-appears, with hidden options visible).

Now all the extra options should be enabled.
Steps performed on TV or PC (depends which remote you'd prefer to use)The following steps are optional depending on what you want to achieve
To change TV model: go into Option and Model should be highlighted
To enable extra features: go into Control then SubOption and enable what you want.
10) Once finished changing model or enabling features you need to disable Hotel Mode, do this by scrolling to Control on the main menu and pressing ENTER.
11) Scroll to Hotel Option, hit the RIGHT ARROW
12) The first line says Hotel Mode, hit RIGHT ARROW twice to set Hotel Mode = OFF
13) Turn the TV off by hitting POWER
Those are the steps I used which worked for me, steps 10 - 13 are crucial to returning your TV to normal with the added extras.
I've had mine running as a C8000 for about 4 months now and the only downside I can tell is that when using the media player sometimes the video output completely turns off yet audio remains, turning off the TV and back on again remedies this. This is infrequent but typically works on the second try, minor con in my opinion.
I hope this helps you and anyone else in the future!
Now if anyone can help me with displaying embedded subtitles in mkv files for display in the Media Player via DLNA I would be very happy!

*Edit I just revised the instructions, had to download the tool and make sure all the steps are correct (my tool version was outdated). I didn't change any options but I can confirm that the model and extra sub options were available for editing.
- Vern
P.S. Working as of 08/07/12 - Feel free to ask any questions I'll help if I can.
This method worked for me but may not work for everyone, no reason why it shouldn't but best of luck!
One thing to consider while doing this is your Firmware version, this program is said to work on any version however I downgraded mine to "T-VALDEUC_0000". I have performed the above steps on both the 3000+ and 0000 firmwares and its worked each time, I can provide the 0000 firmware but it can be found via Google.
Edited by Vicousvern - 7/8/12 at 3:43am