Welcome to the forum.
That's an annoying situation, but let's try to get it working again.
first, I'd check the HT fuse. the mains fuse will be fine as otherwise the amp wouldn't power up. the HT fuse is the small round fuse holder on the back panel near the power socket. if you suspect it's blown, get another fuse that's identical and try that (it's very important you get the same rating, which is printed on the amps back panel. it's something like T500mAL250V, but please check it). if it was blown and you replaced it but it blows again then get it serviced (see below).
if the fuse is fine, try reseating all the tubes. first you need to make sure your amp's safe to work on. you should check for yourself the safety procedures for working on tube amps, but at least you should have the amp off, unplugged from the mains, and then turn the standby switch to on (leave teh main on/off switch to off). this should discharge the caps. do that for 10 mins and turn it off. now reseat the tubes (pull one out at a time and put it back in). be careful when doing this and even though you discharged the caps, as a further precaution DO NOT touch the tube pins as you're pulling them out or inserting them. and DO NOT touch the tube sockets with no tubes in. If you're concerned about your safety, due to the high voltages in tube amps even when they are turned off, then have Line 6 service the amp.
So, after reseating the caps... does it work? if not set it serviced.
how to get your amp serviced. Well the store you just bought it from may be able to help, so perhaps call them and tell them it's DOA. if they suggest a service too, and they aren't a Line 6 service center, then you'll need this link: http://line6.com/service_centers/
Please come back and let us know how you got on with checking the fuse and reseating the tubes. and whether you needed to get it serviced.
Thanks for the quick answer...I really appreciate it.
I called the place where I bought it (American Musical Supply) and did a little trouble shooting with one of their techs. After a 15 minute conversation and trying a few things (the guy was very nice and seemed to genuinely want to help me), they concluded it's DOA and just one of those things. He emailed me a return shipping label to send it back UPS and they're sending me out a new one today.
Although I was bummed that my new amp didn't work, I'm glad I found the forum here and enjoyed reading a lot of the posts. I'll definitely be back to read more on the DT50 and the HD500.
that's great, and glad it's all sorted.
just remember this is a support forum though, so there will always be a certain number of issue threads with any product (just like there is on the marshall forum).
Fro what I see the DT series amps are very reliable based on how many Line 6 has likely sold. I certainly love the tones they give me when I play live.