From time to time I find that I lose the audio engine.  Reset doesn't work, reboot doesn't.  I also have Guitar Pro 4 on the PC and use Cakewalk UA 1G with ASIO. The PC is older Pentium 4 with 1.8 GHz and 2M RAM but it's OK for my limited use.  What I have done in the past is uninstall and reinstall the whole program but that is 30 min plau.  Anyone have any ideas?  It works fine when I shut down one day then a week later, I restart and have no green light in the audio engine.

I remember using a Pentium 4 with 2 gigs and yes, the audio engine would turn off quite frequently. Sorry I never solved the issue but I think I used to bypass the EFX bins while working and pray it would make it through to mix down. I also remember having issues using even the TTs1. I wrote it off to the crappy driver for my interface. 

This Toshiba Laptop I just scored for free from a friend is a P4 and I scrounged up a 1 GiG stick of RAM so I have 1256MB. I was going to install Sonar 8.5 32 bit and use it for just live recording. Trouble is I know my Tascam interface will not be happy with 32 bit XP so I might have to purchase a basic 2 channel interface. 

The most likely reason for the audio engine shutting down is dropouts. If the engine goes too long without data it shuts down. A less-likely cause would be errors raised by the interface driver. 

Try increasing your buffers, which will reduce dropouts. You can bump them up pretty high, since the resultant latency will not be an issue for live recording.