A quick way to have Pidgin connecting to Yahoo messenger server again is to change the Pager server setting for the Yahoo account in Pidgin.
To do this, from Pidgin:
Manage Accounts (Ctrl + A)save and restart Pidgin, Then try to connect yahoo messenger. It works for me.
Select the Yahoo account from the list, and click Modify
Click on Advanced tab, under the Yahoo Options, in the Pager server field replace scs.msg.yahoo.com with cn.scs.msg.yahoo.com