Yay, fun. I too now have to send my 360 in.
Last Thursday I downloaded the demos for Monster Madness, Command & Conquer 3 and Mini Golf. The 360 sat dormant for two days until Saturday when my wife went to play Viva Piniata while I slept off some Friday night antics. Later that day she tells me something is wrong with the 360, that it kept freezing on her, and that it started as soon as she'd gotten the Chippopotamus in Viva.
I ignored her woes until I went to play my new demos on Sunday, only to find that it was true. With the exception of Lumines, every game I try to play will start and then a quick sound of static comes through the audio and the screen immediately freezes. All demos, all other arcade games, and all disk games.
I deleted the new demos and let the console sit for a couple days until I had time to deal with it. Tonight I got on, and still the problem was there. I reformatted my hard drive, cleared the cache, and did everything that
Xbox.com instructed to do. Still, nothing.
I called Xbox support and they're sending me a box to send it in for repair. Yay. No 360 for like 3 weeks. Fantastic.
Well, at least I have Tetris on my phone, and I know Lumines at least works....
It's all fine and good, my warranty is still valid until December of this year. What worries me is what happens after that? The guy told me that the charge for repair is normally $139 plus shipping. It does not give me a warm and fuzzy feeling to think about having a hardware failure less than 6 months into my 360's life, and in 7 months I'll be without a warranty.