Hey there.  Total analog old dude here who just got Sonar X3 for Christmas.  I had it up and running with ASIO driver mode and Realtek in and outs working perfectly.  Now, it won't even recognize the Realtek drivers in ASIO, only in WASAPI, and I cannot hear a thing.  Also crashes a lot.  If I try to  elect ASIO for the driver, the devices are completely blank.  I know it's a weak excuse for a sound card, yet everything was working.  I could record guitar via the line-in, import audio, and it all sounded pretty cool.  Now, when I try to play the AudioDemo.cwp, it's either "busy" on all tracks or looks okay--but now, no sound. 
 
Thank you in advance for any help.
 
(WMP works fine; audio CD and mp3s play well)
 

~Intel DG41RQ LGA775 motherboard~ (Realtek HD Audio)
~Intel Pentium Dual-Core E5400 2.7G  central procressing unit~
~Corsair 1Gigabyte (x2) memory cards~
~Seagate Barracuda 7200.12 7200 RPM 250GB hard drive~

If there are no devices listing after selecting ASIO mode, that indicates there are no ASIO drivers seen by SONAR. This could be due to a corrupted or missing driver. Alternately, the driver may be in use by another application. I was under the impression that MME mode was the most reliable for Realtek chips.

Thank You!  Works now in MME.  A mystery why ASIO worked, then didn't, but I anticipate bizarre surprises as I wade through.  

You could go to ASIO4ALL.com & download their drivers. Then select them in X3's properties page.