Hard Drive Converted to Storage Drive, where’s the rest of my space?

I read up on missing hard drive space forum, but it didn’t help. I have a 300 Hard drive that was partitioned to read as TWO(2) drives on my old computer. I now have a new computer and decided to use the 300Gig as a removable storage drive. I removed and enclosed the 300Gig drive as a removable drive. My Problem: My new computer and laptop are reading and displaying only 128Gigs on this drive. When I checked Disk Management it shows a capacity of 289Gigs(300Gig), but a volume of 128gigs. When I check properties, it only shows my old Windows Operating Files. I’m missing all my pics on the other section of the partitioned drive. HOW CAN I ACCESS THE REST OF THE DRIVE TO GET MY PICS AND SUCH?