Steady loud hum on all mpc outputs... ground issue??

I have an mpc 1000 & presonus firestudio interface. Been using both together, each plugged into different outlet, for months with no problems, no noise. I got really busy and didnt use my mpc for a month or so, it sat unplugged. (possible important note: at one point it was knocked off a table and took a pretty good fall)

So I'm ready to work, I plug it in and set it up just as before and now I'm getting a very loud constant hum out of all the outputs. Hum is present whether turned on or off, as long as its plugged in. I've tried different power cords, different cables (balanced, unbalanced), I've tried multiple outlets, plugged the power strips into each other, every combination i can think of. I tried running the mpc thru a roland 404, still get buzz. Nothing kills the hum, unless I unplug the mpc. & It's a rather loud hum.

Is this a ground issue? If so why did it just start, the setup was the same as before when there was no hum. Did the power supply go bad? Did something break or come loose when it fell that could be causing the hum?

Also, I don't hear the hum through the headphones. Also, I was able to record beats from mpc into roland 404. Then i uplugged mpc and played the mpc recording from the 404 to firestudio w/ no hum. The hum is steady and does not change w/ change of volume output.

Hope this isnt too confusing... but im confused.... any help????

This sounds very much like a ground issue to me. Especially if its sounding like that mainsy hum.

You get this kind of thing if you get a difference between 0v GND between a couple of bits of gear. It sounds like a bit of DC voltage has got onto one of the grounds on something, & that's probably your MPC as it was dropped. Its maybe a capacitor has failed somewhere in the MPC, a guess would be in the PSU, but it could be anywhere.

I'm thinking that a DI with ground lift could be a work around. Or have a look under the hood & see if any of the Electrolytic Capacitors have leaked and replace them (I once fixed an amp by doing that).

Otherwise it may be a strip down job & selling the working parts on e-bay, or sending it off for repair.

--- Just noticed that you say it does the same when the MPC is turned off . It maybe worth checking out the Presonus. See if your MPC hums if it is connected to a mixer or straight to an Amp. Although you did get the hum on the 404 too.
I wonder if the signal ground is getting to the mains ground via a short somewhere (could still be a capacitor). Try wiring up a plug with only the Earth connected (Carefully - & take the fuse out) & plug it into the MPC, see if you get a hum ----

Its a bit of a sad first post for you dblehman. but hope it all comes right for you & welcome to the forum.