well a MPC will still boot if drive is formatted. OK so since it not doing this then two things to do.
First is to make sure your screens contrast is set right. Sometimes it is too bright to actually make anything out, so turn on your MPC and after 30 seconds or so, hold down stop button and turn jog wheel. It might be that and if your MPCs contrast is set too high you will see nothing till you do this screen contrast correction.
If by chance you have some how erased the OS then I suggest doing the following. Take out hard drive and get a CF card and a USB CF card reader (borrow one or buy one), then put the Akai OS on it and put it in the MPC and then turn it on. This way it should see OS and be able to be loaded into it. I think it does from memory.
When you say demo version do you mean the free version. They all can be demo'ed.
check them here
http://www7a.biglobe.ne.jp/~mpc1000/cept you can not demo the XL screen upgrade one, unless you buy the big screen upgrade of course.