So you're having upgrade issues moving to version 6 of this module. You are not the first. But there are a few things you can do to begin debugging yourself. Posting here with "I upgraded and my blog's gone" is not going to get you anywhere as it doesn't give us any information on what might have happened.

First: check if the data is there in SQL. That will give you peace of mind if it's still there. So do the following:

1. Is there a table Blog_Posts? If not then the upgrade scripts didn't run correctly. You'll probably still see the table Blog_Entries (the old table for the blog posts). You need to roll back your installation to what it was before the upgrade attempt as something has gone seriously wrong during install.
2. Do you see data in this table? If not and you had old blog posts in the module before: see above. Roll back.
3. You'll see several fields in this table. So if there's data you can now begin to trace the data. First check out the underlying content item. For that check the column ContentItemID and open the ContentItems table and verify that there is a record with that ContentItemID. This is where you'll find the actual content of the post.
4. Points 1-3 should indicate whether the old blog posts are still in the database and whether they have been migrated to blog 6. Now we're going to check the wiring to the front end. Check out ModuleID in the record in Blog_Posts and in ContentItemID. They should be the same. Write down that ModuleID.
5. Now go to the blog module on your site and determine the ModuleID of that. The simplest is to click on some item in the module menu and the url in your browser will show either moduleid or mid in the querystring with a number behind it. That is the module ID. Is it the same as the value found in #4? It should be. If not, then you can try manually rewiring the data to that module id or try to find the module if that the data is pointing to.
6. Finally: the module settings govern how data is displayed. It can reduce the selection by blog id, category id, etc. But normally this is all reset during upgrade so it shouldn't limit it. Similarly, you see whatever the template is set to show. Again, by default this should show the data you have. Double check settings.

I hope this helps determine where your issue is. Again: you can help us by being really specific when you have an issue and doing everything you can to drill down.

 Peter