We use Episerver 7 and it seems like the Search field dont work.
I get "no results" when I search pages, block, files whatever.
Anyone have an idéa why?
Probably the search service is not installed on your site. In order to add search service you need to install EPiServer.Search package on your site. Here is more details.
Edit: Sorry, I just realised the question was about EPiServer 7, not EPiServer 7.5.
As @Sergii says, the internal search requires you to install EPiServer Search.
If you downloaded EPiServer 7 and ran setup.exe, you should be given the choice to install the EPiServer Search service.(Otherwise you can run EPiServerSearch.msi from the EPiServer 7 zip file manually)
You should also be given this option via Deployment Center. Have a look at this blog post for details:http://sveinaandahl.blogspot.no/2013/06/how-to-install-episerver-search-for.html
Once installed, log back into your site and go to Admin > Config > Search configuration.Make sure Blocks, Files and Pages are checked.