Kbbaucom, the paint came off because your friend hadn't prepped the surface of the case properly.
First take the case off of the computer.
using 1000 or higher grit wet/dry sandpaper from your automotive store, wet sand the parts you want to paint. then prime them. two coats. Then lightly wet sand again. 5 coats, sanding between coats. then paint your color, sanding between coats. 5 to 10 coats.