Sound works fine - there is no picture...

looking online as i have same problem, sound without picture points to T CON board. approx $50-100 part + labor

Old age failure

This can happen for several reasons. I am guessing that you have the sound card and driver software installed correctly.
Many times this is caused by Windows not using the new card as the default Sound card. Since you have not mentioned what operating system you are using and didnt mention if you have an onboard sound card with the new card, take a look at the instructions on the page below. It gives instructions on how to set the new sound card as the default card.

http://icompute.info/no_sound_from_card.htm

Maybe this will work. Hope so...

The ballast hardly ever goes out on your model. Its more likely failed capacitors on the power board which is the cause of the solid red lamp led. Heres alink to the repair kit for your model and it contains the replacement capacitors and step by step instructions with pictures.
http://servicemanuals.vstore.ca/product_info.php/pName/mitsubishi-v26-dlp-power-pwb-repair-kit/cName/repair-kits

More likely its one of the Video output ICs which are located on the three CRT drive boards. I have seen that happen when one of the ICs fail they are TDA6111Q heres what they look like they are attached to the aluminum heat sink on the drive board

Your control board seem's defective or the inverter board (associated circuits) are bad. This is common in most TFT-LCD Tv's.......

I have 8.5" TFT widescreen Monitor Portable for three years. Now when I turn it on, it only has sound, the picture only has one second blink, then dark.
I am now in Shanghai,China, is there a service in Shanghai which I can go physically to get it repaired?
xujingcan

PROBALLY CUZ URE CHEAP *** AINT BUYIN D RITE CABLES N ****

There is a small switch on the right side where all the audio/video ports are. If that switch is forward in the "video-out" mode, the onboard (TFT) screen is shut off. Move the switch back to "TFT" mode. Hope this helps.

Sounds like you have a short somewhere, probably the Horizontal Output Transistor. If there is a fault the led you mentioned probably should be blinking. You probably are going to need a tech to look at this as it is a very complicated process of elimination.