Okay, this happened to me earlier, and I asked the help desk people, and this is the reply I got:

Basically, what you are seeing is an IP ban. This ban does not target you, but had to be issued temporarily because a certain user from your Internet Service Provider violates the policies quite badly and keeps harassing members, while creating new accounts to continue their harassment. So our only way to stop this user is by placing an IP range ban on the Internet Service this user is using. Since this prevents new users from joining deviantArt, IP range bans are rarely issued and usually stay only for so long, until we can be sure that this harassing member is staying away from deviantArt.

It's very common to share IP addresses among customers on many Internet Providers, thus it's not always possible to make a ban in a way it only affects the harassing member (since on the next dial in, they would get a different IP address - thus we are left with no choice than to ban your Internet Service Provider's IP range to protect our members). We regret that such steps are necessary and apologize for any inconvenience we may have caused, but sadly enough, sometimes this is simply the only choice we have left.

There are, in fact, three ways you can create an account, despite your Internet Provider being temporarily banned:

The first one is the most inconvenient: You wait for the ban to expire. IP range bans don't stay forever, and they will be removed at some point.

The second one is easier: You ask a friend who is already on deviantART to create an account for you and hand you the username and the password. Even though the IP range you are using has been banned, you will be able to log on to the account that has been created for you just fine. Also, you can also sign up from a different internet service, from school, work, or ask another friend who uses a different Internet Provider to let them access the internet for a few minutes and sign up. Once created, you can log on to the account just fine.

The third way is, when you sign up, you are asked if you want to subscribe. If you say yes, and subscribe to deviantART, the IP Ban check is bypassed, regardless of subscription length. The idea behind this is that people paying when signing up for new accounts are less likely to harass, since they wouldn't pay just for having the chance to harass (and in consequence getting their account removed again). Once created, you can use the account, even if the subscription expires.

I hope this information is helpful, and again, we apologize for the inconvenience. Hopefully one of the above outlined methods is feasible for you, and if you have any more questions please feel free to ask. Thank you.

So just go attack a friend or a library or something, and make an account there. Hope that kinda helped...