try making the same ID as even if it has been stolen it seems it has been deactivated "and yet it is deactivated as it's not saying wrg Usr & Psw" so try making urself the same Id ...
and abt deactivating an account "as ur topic's tiltle says", well its so simple ... check this link
To deactivate an account DO NOT SIGN IN!anyway, if you still hadn't formatted ur pc and you wanna get ur buddy list back try this ...
C:\Program Files\Yahoo!\Messenger\Profiles\UR ID\Archive\Messages here u'd find all of the Ids u'd added incase you had activated the archive.
However no way to activate a deactivated account back, yet ur log files will be kept at yahoo servers for 90 days after deactivation.
If ur old ID is no longer available I guess u had been hacked by some1 who wants ur ID! .. get a superscan and check ur system for unpatched exploits like 445 or 135 - usually are used to hack ur pc when are volnurable -simple exploites-, remember if you had signed to ur mail by some sort of links "decoded links whom'd divert u to the link i provided earlier, or if u had received something from someone lately.
sorry to be late as I only was told yesterday ...
hope I had helped ... take care