If you have an older version of Partition Magic, which is very likely since it stopped development in 2003 when Symantec bought it, it doesn't know anything about modern large disk partitions and doesn't run on Windows 7 or know about Win 7 paritions (unless started from a Win XP disk). It will report problems with the partition table that are not really problems, and then if you allow it, will corrupt that table as you observed. You can potentially attempt to manually edit that low level table, but it may not be easy to guess the right values. Other utilities can't recover from this type of catastropic corruption because they expect an intact partition. A drive recovery service could manually get most of the files back, at a very expensive price.
Since its a new system, I would accept it as a loss, and use the Win7 install disk to repartition the drive in advance mode. (creating 2 paritions, one for win7, and one for other use). Then recycle the PM disk. Good luck.