migation assistant does not find users on original imac

I am trying to migrate users from a 2006 imac (OS snow Leopard) to a new, (new to me - refurbished) 2013 imac running mavericks. Migration assistant connects the 2 macs, but does not find the user accounts on the old mac. I thought this was because I have set up myself as a user on the new mac using the same apple ID before doing the migration. So I deleted user account on the new mac& still nothing - had to change account from admin to standard to delete (left my wife's users account as admin). Still nothing. I changed the user account name on the old mac to a different name - still nothing so I changed it back (on both the old & new macs I had used same user account name but deleted it from the new mac). Nothing works.

Could this be because the old mac (snow leopard) thinks it has already done the migration? Should I re-create my user account on the new mac & try again? Or is there any way I can go back to the factory set up (Mountain Lion) on the new imac & start from the set up again? I'm stuck & I'd rather not go to the apple store.

If I'm not posting in the community, please point me to the right one.