page up > page down > blue should bring up the small diagnostics menu on all STBs regardless of flavour.
There should also be two lights on the right hand side of the display - the top light is for power - the 2nd light down is for return path (connected to ntl) - the 3rd light is for the remote which will only flash when receiving input from the remote.
Pressing the help button should bring up the help menu
Occasional reboots are not too much to worry about - upgrades to the code on the STBs happens from time to time or for changes in your DiTV packages. On the other hand NIT being displayed is not too hot. Usually means really bad signal levels or a b0rked box - both of these issues will produce dodgy interactive services too.
Have you called CS to have a gander at the box from their end? They can have a look at lots of information regarding the signal levels and suchlike which might shed some light on it.