Your Question: "how can i see my old yahoo messenger messages as now i am not able to view in my archive folder as well...but i want to see as it an important messgae...please help me out..."

Yahoo Messenger does have a log but you can simply access this either from the user who's previous messages you want to retrieve. So, click on a user and at the top of the dialog box, there should be a link to "Recent Message." Alternatively, you can access the archive log from the "Contacts" within the main Messenger application window. This is menu item is called "Message Archive" and you should be able to access all logged conversations.

Hope this helps.