OK the system disc is very hard to find unless someone has got one on ebay etc but the good news is that Roland have it here:
http://www.roland.se/supp...ates/General_Apps.aspx Here too I think:
http://www.roland-museum.de/synth/html/MC500/Roland_MC500_downloads.html On the Roland site there are two things. The actual system disc file and a little program that allows you to make the system disc. Now I am not sure but it might have to be on a 720K floppy not sure about that. You will need a computer with a floppy drive of course. (What is that!)
I had an MC500 too but got rid of it recently but I was able to make the system disc Ok and the unit worked OK. You have to turn the unit on everytime with the system disc in the drive. The OS takes a while to load from the drive.
One the OS is loaded in you should be able to put your song disc in and load it up. I would do that and connect the MC500 to some synths etc or GM synth to make sure the music plays OK.
Then you will connect it to an available midi port connected to your computer. I guess you are using Sonar. You will have to put the MC500 into external sync mode and also transmit the midi clock out that port. This does not normally happen in Sonar and you have to instruct it to do this.
Then when you start Sonar the MC500 should start and stay in sync. Then you can transfer the sequence over and save it is a SMF.
Let me know is the system disc thing does not work. I remember finding it somewhere else as well as the Roland site.
The old Roland MC was quite a good sequencer. Make sure you make the right System disc too. because there was an MC500 MkII that might have had a different operating system.