For some reason my previously recorded tracks (under the same project) are now being recorded in my new track. The effect is basically layering one recoarding right on top of the other one.

It wasn't always like this. Everything went south when I loaded a new driver for my sound card.

Any advice would be great. Thanks in advance.

Try going to control panel/sounds/recording volume and check that you don't have STEREO MIXER selected

depending on your sound card, you could have a setting that allows you to record what you hear. Hence, you record a track and as you play it back to do track two, it records the original over top. Usually this causes the second track to sound distorted if the volume(s) are too high.

my problem is not any of these. I have recorded on one track, and if I select record (R) on any other track I see the signal from the first track on any other track. Any thoughts why? I use Sonar Producer 7 with an EMU-0404, and a Mackie ProFX16 mixer.

As I recall, the E-Mu software mixer is not very intuitive. I'm pretty sure you have a routing problem similar to What You Hear and Stereo Mix. I don't know where those settings are.
Also since you wrote "my problem is not any of these", why didn't you start your own thread instead of resurrecting a 13-year old thread?
Anyway, you're here, so do a little research yourself on the web until someone who knows E-Mu shows up (which might be awhile since this forum isn't very active. Try the SONAR forum , too, since you're using SONAR. This is the Music Creator forum, a product that has been discontinued.