Go to Management and go to Disk Management, then delete all partitions on this drive. When it shows black with no partitions and a number close to 500GB available such as 485GB, create a new partition in this space. This will then prompt to format the space NTFS etc. When completed you should have around 485GB of space available if the size stated by windows disk management was 485GB.
If this drive is your C: drive ... LEAVE IT ALONE!!! If its a slave or external and no data important. Blow away the partition and start fresh with instructions above to do so.
This 100MB partition may be because this hard drive had say Vista OS on it etc and more info here:
http://www.techedze.com/Thread-hide-the-windows-7-100mb-system-partition-in-vistaThe only other time I saw something similar other than OS drive is when its an external with drive data security enabled and you dont have the password. The 2nd partition with the information is hidden and you only see the primary partition where the drive data security interface resides. A Western Digital drive did that to me. I set complex password. Didnt use drive for 9 months or so and went to access it and couldnt remember the password I had used. I ended up blowing away all partitions and started fresh without the data security interface to get my 1.5TB back.
