Where did 100GB go?
You could try $ sudo du -sh /* to get an overview of everything taking up space on your drive. It sounds like you might have partitioned your drive down to a 56GB volume, even if you don't have the other 94GB allocated to a different partition.
You can use utilities such as KDirStat to visualize where your free space went.
WinDirStat and Disk Inventory X are similar tools for Windows and Mac OS X, respectively.