I already told you this via mail but I'll add it here, too so others will find it in future.
This is from our new FAQ:
Back In Time prior to version 1.1.0 had an option called
Auto Host/User/Profile ID (hidden under General > Advanced) which will
always use the current host- and username for the full snapshot path.
While (re-)installing your Computer you probably chose a different host- or
username than on your old machine. With Auto Host/User/Profile ID activated
Back In Time now try to find your Snapshots under the new host- and username
underneath the /path/to/backintime/ path.
The Auto Host/User/Profile ID option is gone in version 1.1.0 and above.
It was totaly confusing and didn't add any good.
You have three options to fix this:
Disable Auto Host/User/Profile ID and change Host and User to match
your old machine. 
Rename the Snapshot path
/path/to/backintime/OLDHOSTNAME/OLDUSERNAME/profile_id to match your new
host- and username.
Upgrade to a more recent version of Back In Time (1.1.0 or above).
The Auto Host/User/Profile ID option is gone and it also comes with
an assistant to restore the config from an old Snapshot on first start.