Sound Card disappeared from device manager, reappeared on restart

About 20 mins ago my system froze and my headphones turned to static when I rebooted the PC windows loaded and my sound card was missing from device manager. I did a check of the system files and got a all clear, so I rebooted the PC and it magically reappeared and started working again.

My sound card is a Creative Sound Blaster X-FI Titanium Fatality and I have driver version 2.17.2008. Now I noticed there is a new 2.17.2009. What would make a sound card just stop dead and then just start working again? The system is two years and I have a Realtek HD audio device and a AMD HD audio device also showing up in device manager. The Realtek and AMD are both integrated into the motherboard but they all worked fine together for two years so I never touched it. I guess I should be happy it's back, but I am wondering what occurred.