Try manually scanning the frequency for those individual channels after 7 p.m. That is when BBC 3 & 4 usually start broadcasting.If you do it before that time you will get CBBC & C Beebies. To do this,go to one of either of those channels,press the INFO button until you see a bar at the top of the screen displaying the frequency number.(They both broadcast on the same frequency) Then press MENU & go to the installation menu,go down to the frequency that you require & press OK, a small tick will appear to the left of the bar,then press the button for MANUAL SCAN. It will take a couple of minutes but it should do the trick.
J.Deacon, October 2008