Noise from all outputs but the phones

Hello everyone,
I have just finished fixing all of my cables behind my mpc, mixer, turntable and when I plugged everything back in I am getting this loud noise(almost like a ground noise like if I took off the ground cable of my old 1200 from the mixer) from my main outputs. The noise persists even when the mp is off ..maybe a bit less.

After trying different cables I tried to plug the mp to my mixer with a Y cable using the phones output..and the noise is gone.

I hope I explained myself well enough, thanks in advance to whoever can help.
M_

Are you using balanced cables? It sounds like maybe no if the hum is still present through the mixer even with the MPC turned off.

The phones output would be largely immune to picking up a ground hum with the connector have tip/ring/seal connection.

Try to check it with both unbalanced and balanced cables, that's the first step in trying to isolate the source of the hum. (likely external and being picked up by your cabling, if it is that balanced cables would reject the interference.)

Thanks for the fast reply:
I am now using mono instrument cables. I will try using stereo cables.
Sorry for the noobish questions xD

No problem we've all been there especially in the beginning. Yeah those instruments cables are definitely not grounded.

If you need to purchase balanced cables and are in the US, do not go to Radio Shack. Their 1/4" cables are ungrounded and at my local one not a single employee even knew what one was. Guitar Center sucks but at least their cables are labelled and even their worst employees understand the difference.

If the issue persists a lot of guys here are far more saavy in electrical matters than me, so just give as much info as possible and people will try to help you.