You've been posting this same complaint for several days, without any variation. Here's the bottom line:
1) The numerous duplicated cross-posts aren't helping you. In fact, they may cause many of the more knowledgeable people here to avoid you.
2) You really haven't described this problem anywhere. You've just said you have "flickering light through the screen," but I don't really know what that means. You seem to be assuming this is a hardware issue, and it certainly sounds like it could be, but without a clearer description we really can't offer you anything new that hasn't already been said.
3) If the tech at the Genius Bar can't see the problem happening, they can't really do much for you other than send it off for service. It is your choice whether or not to accept that service, but if it's a hardware issue, choosing not to have it serviced will mean choosing not to fix the problem.
4) You seem to be balking at the idea of buying a hard drive for backups. If you don't already have a hard drive that you're using for backups, you should get one regardless of whether you send the machine off for service. Without backups, it's just a matter of time before you lose some, or all, of your data.