If you have ever used yahoo messenger on your comp. then you will get your password back. Though not 100% there is a very very high change. You can use one of the below software to recover your password.
In case you have recently formated your system then chances of recovery seems to be very less.These are IM pssword recovary softwares.
Trial downloads, only 4 chars reveled
Spyware free !00% safe
Instant Messengers Password Recovery Master
Advanced Instant Messengers Password Recovery 3.4