Curata registry cu CCleaner.
http://www.piriform.com/CCLEANER
Da un restart si instaleaza YM.
Instaleaza de aici -> Yahoo! Messenger v 11.5.0.155 [OFFLINE] [18.3 MB / Windows All] - http://fbx.ro/ksdk5e1em7c76qg8 sau http://www.softpedia.com/......nger.shtml