I think I'm having the same problem.  I have a brand-new XPS400, TV tuner connected directly to the cable outlet, and every time I try to run Live TV in Media Center, the app simply closes down.  I spent 3 hours on the phone with tech support the other night, and nothing they did helped. The guy I spoke to told me he was going to escalate it with his boss, and I'd get a call back the next day.  It's now 2 days later and I haven't heard anything.  I'd get some 3rd party software to run live TV, but what concerns me is that Media Center is part of the operating system, and if it's not running right on a brand new computer, what are the odds of something bad happening later on.  Pretty good, I'd think.

When I first ran setup for Media Center, I kept getting error messages like:

Critical Media Center Process unexpectedly failed. If problems persist, please restart your machine and try again, or contact technical support. Code 1.  After Code 1, I'd also get Code 3.  Went thru all this with tech support, removed rollup, reinstalled a bunch of stuff (some even at DOS level), and still no joy.

I spent $2,000 on this computer and part of why I bought it was the TV tuner for live TV. I'm thinking seriously about disputing the credit card bill when it comes in, unless I get a resolution before then.

Me again.  Well, I spent a couple of hours on the chat line with Dell yesterday (BTW, thanks to this group for recommending them--I found them to be much more knowledgeable & helpful than the phone support!).  Anyway, after exploring a few things that "might" fix the problem (updating drivers, removing some eHome files), we decided that the best thing to do (ugh) was to restore the computer to its factory settings.  The process was simple and the good news is that it fixed the problem.  It did take a couple of hours to get the computer configuration back to the way I like it to operate, but so far so good. I've got live TV, all the channels are programmed, and I'm getting ready to try out recorded TV, etc.  Of course, going back to the beginning is easier to do when you have a new computer. It was also really helpful to have a separate external drive for backing up all my data and downloaded programs & settings before I did the restore.

Good luck!