There are several reasons why a partition table is damaged. One reason can be experimenting with disks, for example, applying a slightly modified (may be mistakenly) command to make a USB flash drive bootable (for a live OS). It can also be possible by some faulty usb creator software. Additionally, directly writing an ISO using 'dd' command can result a corrupted partition table. The partition can also be damaged or engineered by a virus to meet certain goals. As these operations are mostly run on USB drives or USB keys this post provides instructions to fix such partition tables. Generally these commands are applicable to any kind of hard-disk/usb drive.
This article includes instruction for both Windows and Linux. However, for knowledge, feel free to explore the article.