Oh, no!! You have to return that disk immediately. DO NOT USE THE COMPUTER!!! The disk shows only 465GB because a mad cow ate part of it, and if you use it you could get sick. It's a known problem with WD disks, most of them do that. Return it!!!
Edit: OK, just kidding. There's no problem. WD and Seagate and so on claim a disk has 500GB if it has 500 *10^9 bytes. Microsoft thinks 500GB means 500 * 2^30. Run it in Calculator: 500,000,000,000 bytes, divided by 1073741824 (bytes per gigabyte, as gigabyte is defined by Microsoft), you end up with 465.661.
Your operating system and swap file take the difference between 465 and 427, that's why only 427 GB are free. It all looks perfectly normal, don't worry.