I installed 1 year ago ubuntu 17.10 alongside Windows 10 boot manager and ubunut 17.10 stopped working suddenly, ubuntu boots normally but it gets stucked at the logging screen which won't let me in , so I want to uninstall it and install it again without damaging my Windows 10 partition. Where do I begin? What should I do first?
Download a new ubuntu image (pick ubuntu 18.04 since the 17.10 release will not be supported anymore in few months).
When booted in the downloaded image, just choose to overwrite the current ubuntu installation. You will loose all ubuntu 17.10 data and have a fresh 18.04 installation. Windows would not be touched.
You can follow this guide for the installation.