Seeking help for original gameboy

I recently have found an old original nintendo gameboy which I really want to fix.I sent it to my friend who took it apart and he managed to clean and fix it a little. Since I don't have a game for it I can't test it.Basically when I turn it on the power turns red and nothing else happens. The system is mute and the only visible thing on the screen are two horizontal thin black lines, one on the top and one at the bottom. Sometimes they appear and dissapear.If anyone has any idea to how can I fix it I would appreciate it very much. Thanks for the tips in advance.