Often on this forum page people will ask how to connect a new light after they have taken the old one down. Folk assume that because it is a light it must be wired in a "standard way" and all they have to do is to ask which coloured wire connects to which terminal.
I have to admit, it does sound a reasonable assumption, but sadly it is a wrong assumption. The "problem" arises because it is up to who ever did the initial installation what method they chose to use, and to complicate matters, what colour of wiring they chose to use, particularly when you get a 3 core and earth cable which has Red, Yellow and Blue cores (and a bare earth)
Another thing is at a standard ceiling rose it is not unusual to have 3 cables (9 wires in total) One cable is "supply in" another is "supply out" the 3rd is "the cable to the switch" Unless you know which is which, get it wrong and you can get a loud bang and no lights at all.
That is why BEFORE you take down a light, you should mark the cores (Most mark with increasing numbers of stripes) then take a clear in focus picture of the cables and the connections, then check if you can see the picture.
If you look through the posts on this page, quite often we can not help other than to say you need an electrician to visit you, the electrician can then test the cables to establish what cable is connected to what.
Sorry about that.