Humor me:
What disk are you trying to use? I know you said that it SHOULD work, but if your are new to the Amiga, there are good disks and there are good BOOTABLE disks.
Also, if your trying to boot a NTSC program on a PAL machine (and the other way around), you can get the same out come.
Confused yet?
Don't worry, we'll do our best to get you up and running.
Just give us a run down of what you are using and what you've got. And if you don't mind, maybe a bit more information on the A1200 you got from you friend (ask him)...