What version of OS X are you running ?
What is the format of your old PC Hard drive ( NTFS, FAT32, something else )
Is that old disk build into an enclosure and connected to your Mac via USB ?
Is the old hard disk ( once connected ) visible in DiskUtility ?
Is the old hard disk ( once connected ) visible in the Finder ?
Can you see any file at all on the old hard drive or just your personal files ?
You don't need Paragon NTFS to read NTFS formatted disks, only if you want to write to the disk.
Cheers ... McBie