Hello Chiara,
Welcome to Geneva,
The process of looking for a room in Geneva is quite difficult and it might take some time and effort.
Make sure that you checked constantly the classifieds section here in glocals,
get yourself registered in http://www.easywg.ch/ webpage and also in http://www.cagi.ch/en.php which provides a quite good service for students and trainees.
You may also want to check these sites:
www.expatriates.com
http://www.craigslist.org/about/sites/#EU
http://switzerland.gabinohome.com/en/rent+room/geneva
Just try to work on the room searching every day, be very proactive and keep track of the people you contact. And, please, be very careful with Scams, there are a LOT of theme around. If it sound very good to be real, usually it is a Scam (Usually, because it was not my case).
GOOD SEARCH!
AND GOOD LUCK!
