sounds like a hardware issue. the typical diagnostics are:

try the working turntable/cdj on the broken side? if it works, than its your turntable.
if no turntable/cdj works on that side, than it's the box.

What mode where you using?

You have most likely lost one of the channels on the left deck. Go to set up to see what side you lost. You can do this by playing a track and watching the horizontal or vertical line. While playing a track and in the setup menu. Pull out either the RED or WHITE cable from the turntable to see which side you have lost.

Try each step to see if the problem persists on the left deck or transfers. If it persists, revert the step to the normal setting;
Swap the RCA cables of the turntables first (red to white and white to red).
Swap the inputs of the turntables themselves.
Next, try the RCA cables from the scratch live box to the mixer. (TTM57 move to next step).
Swap your needles.

thank you gents; I changed RCA cables red to white, white to red deck plays normal now. you guys are life savers. Glad to have you in my corner. Time to get busy. DJ Reel

Yo R2R... Make sure it was a set up issue and not a needle issue or this will occur again.