Zahra, this is your hosting issue, they must have not allocated enough resources to run PHP server, besides serverpars does not have a very good reputation in community, I mean just look at their prices $6 annually? really? Where moodle does not require high resource server, but at the same time do not expect it to run with resources good enough to run a static HTML page.
Consider changing your server, else you'll be wasting time on installing moodle.
Clément, have a look at this video tutorial, shows how to set up OpCache on Windows server platforms.
http://blog.academictools.org/2015/12/installing-moodle-on-microsoft-windows.html
in Adaptable theme general settings you will be able to find front page content, adding anything to it will show up on front page.
Nothing happened to apache, dont worry about that unless you had played with apache settings.
yes do the re-install and you are good to go.
Wouter,
here are some videos that may assist you in upgrading moodle, specially the last one
http://www.screencast.com/t/7di1TIv9NH
http://www.screencast.com/t/isCbx6rnVd
http://www.screencast.com/t/QfsROwJCz
http://www.screencast.com/t/p59D8pnX8h
http://www.screencast.com/t/BKK0rRLd1
http://www.screencast.com/t/ZtdiUTSrItGX
and if you want to make clones of moodle will also be helpful towards upgrading
http://www.screencast.com/t/aLYYluO8qs