Okay, just a wild guess, but it's probably an electrical fault in your power supply. Unplug the laptop and don't attempt to plug it back in or turn it back on. Your data should be okay, but there are no guarantees. You don't have any backups?

You need a converter cable to hook a laptop hard drive to a desktop, so go buy one of those. Fry's sells them for ~$10 US. Hook your laptop drive up as a second HD on your desktop and make a good backup.

If the drive doesn't show up check the name of the maker on the case and visit their website on your desktop to download their drive tool set. That's the best way to evaluate if the drive survived. Run the tools, usually you copy them to a disk and boot from it, and cross your fingers.

Good luck.