Restoration problem from Dell back up

I have an Inspiron 3521 (windows 8) and I used Dell back software to back up my data to an external hard drive. Recently, I had to reformat and install Windows 7 (professional) + Ubuntu. Now I can not restore my previously backed up data (stored in .inp format). I downloaded and installed the dell 'backup and recovery' software but it can not detect any archive from my external hard drive. Can anybody indicate how to retrieve my data? Thank you in advance.