This happened to me also.
CDP assigns a key to each computer. The program recognizes your computer based on some information obtained from its operating system. So, if after the crash you've installed a brand new version of the operating system, your previous key will no longer work. If this is the case, you can send them an e-mail with the confirmation you have received from prometric (so that they know you're really planing on taking the test and you're not trying to get a new key to sell it to someone else). Tell them what happened. They will charge you 19$ and assign you a new key.
If you haven't installed a new version of the operating system, however, you can simply login to your account on their website, download the setup file, and obtain your key. Then, simply install the program and use the key to unlock it.
Hope everything works out for you!