uninstallation SQL server 2014

I installed sql server 2014, but after six months this version has expired and logically it should be a registred and not a trial version. 
I decided to uninstall and reinstall, but some services could not be installed as the engine of the database, the analysis services, reporting services etc. 
I tried to install sql server 2012 and I had the same problems. 
thank you for your understanding.