No problems on my 360's so far but I have fixed a few for people, one is still working and one packed up after about two months, and NO! it won't get you banned if you fix it yourself lol,
And yeah, the 360 did start out very "dodgy" but the problems have almost completely gone now specially in the newer units,
I'd just go onto xbox.com, book it in for repair and let them sort it for you, it won't cost you a penny even if it is over 3 years old, lots of threads about this on the internet, MS would much rather fix your 360 for free so you can get back on live and give them money again on subscriptions, games, dlc etc,