HI all - Not sure if its the right thread im posting this!

My sims game works just fine - a little slow, with my cc installed.
I tried to merge som files, but then the game wont start at all.

Any idea why?

Most likely because you merged files.... What files did you merge?
Have you taken out your mods folder and tried the game without the mods folder to see if it works?

I put my CC in folders, so trying to merge them like:
Dining chairs in one package
Rugs in another
and so on.

The game works without the cc and mods, also with them before i try to merge them together.

I would say you have an out of date mod then.... You need to take all mods out (leave cc in) and test game. If it works then add half mods back and test game.
If it wont load then you know its a mod in that half.....Process of elimination really to find which one.
If it loads then take out those mods and place them somewhere. You will then need to use a process of elimination on the other half to see which mod is causing you a problem.

do you mean actually merge? or do you mean group them in the same folder? also not recommend to merge mods (actual merge)

This is a good point, and a "combined" mod (one with both a package and a script) can have loading dependencies, for example either the package or the script must load before the other. If the order they are loaded gets changed because the package has been merged with another then the mod can cause a complete game failure (infinite load, exit back to world screen, etc)

I mean merge them together.
I can some of them to work, when merged. The rest i will leave as they are.