Partition Magic is no longer supported. It sounds like you have SATA drives. From the rescue disk it runs in DOS and DOS has very limited driver support for SATA.
It also does not understand the sector alignment that windows 7 uses and cannot support drives larger than (I think) 1.5TB
Search for "Partition Wizzard". They offer a free version for home use and it works the same way PM did.
They also have a free bootable CD, we always reccomend aking changes to the partitions "outside" of windows.
Always backup your data before any partition work.
Dave