bad migration to J3

Ok, I finally succeed in restauring the site, with the akeeba jpa file and kickstart.php. It's fantastic
But now i'm back to the beginning : joomla advice me to pass to the 3 version.

So now what i should do to pass to the 3 without making the same big bug ?
What about the php version, where do i go to know (and to change) it ?
And about flexi, how do i know that it's the last version ? if it just doesn't proposed to update ?

Ok, php WAS 5.3.29 . It's now 5.5.22
So, you seem to think it could be the cause of my migration failed ?

Hello

about your last message do you mean that you re-upgraded to j3 and it is working now ?

-- since you have PHP 5.5,
backup, upgrade to J3

-- open flexicontent (2) system plugins make sure they are published and re-save them, try clearing cache, and re-login in backend