So a few weeks ago I was having fun trying to set-up MythTV in my flat. I had a laptop  sitting plugged into my TV for a while. I have a Freecom Digital TV USB DVB-T Freeview Receiver  plugged in and working fine under Kaffeine  however Kaffeine is not designed to be used on a TV screen.
I installed MythTV from the repositories and went through the setup. It went mostly without any problems (though some of the questions were kind of difficult to understand) and scanned to find the channels. My first major gripe was with this scan. It took ages! As in hours. Kaffeine manages to scan and receive the channels much faster than that. Surely there must be a timeout set wrongly somewhere.
Anyway – though it took ages, It did manage to find all the channels, I then finished up and attempted to enter the frontend. All good. Now watch some TV. Whenever I selected “Watch TV”, the screen would just go blank for a fraction of a second then return me to the main menu. There is a thread on Ubuntu forums  that explains it nicely however the thread did not provide a nice solution. The only bit of ‘help’ was the comment by ian dobson “What are the frequencies saved in the MySQL database? I had to manually correct the frequency in the channels table using MythWeb.”
This comment was good because it pointed out that yes, whilst the scan for the channels worked fine, it failed to put the correct (or in fact any) frequencies in the database, if is utterly useless because as far as I can tell, there is no method of putting these frequencies in using mythweb. What I had to do was install phpMyAdmin  and edit the tables using that. installing phpMyAdmin also proved to be rather difficult due to the fact that I had not set passwords correctly however that was a hole different saga which I can’t remember the finer details. However I was able to solve that issue with a bit of searching the web.
once phpMyAdmin was installed and I could log in and edit the tables, I found the two important tables were ‘channel’ and ‘dtv_multiplex’. AFAIKT, digital TV is broadcast on about 6 different frequencies (or multiplex) with many channels on each multiplex. When scanning for channels, MythTV failed to insert the correct frequency for these multiplexes. I was able to work out the correct frequencies using Kaffeine. This is the tedious part.
Using the channels table, I was able to find one channel on each multiplex and write it down. Then find the correct frequency for that channel from Kaffeine. Then input the correct frequency into the dtv_multiplex table and after much fiddling and hacking around (some swear words may have also been uttered) it worked!
 Kaylee – Philips Freevents X56
 as shown http://www.reviewcentre.com/reviews96386.html