How can I repair my Android devices system?

[AC Question]

how can I repair my android devices system

I turned my developer options ON and one day I decided to clean my phone... I accidentally deleted some kind of system application... now my phone starts normally but I cant see homescreen and phone tells me all the time ''Unfortunately, System.UI has stopped''... I have tryed to restore the factory settings but it wont work... what can I do? do I have to install some kind of ROM? my android version is 4.2 (jelly bean)... I cant even get connection between phone and PC!!

 

[B. Diddy]

Welcome to Android Central! Which phone, and is it rooted? If you're unrooted, you can't accidentally delete a system app.