I worked all day on getting my first store set up, and after finally going in and selecting a plan, everything completely disappeared and it says "This shop is unavailable" I cant even log in. My shop is thechainplugg.myshopify.com
I've had this issue as well, multiple times. In fact our store broke down just yesterday. Try and contact support through their online chat.
I did twice actually. They just keep telling me not to worry and it will be fixed in no time. I dont understand how I'm not supposed to worry lol.
Arm yourself with patience. I had to rebuild our store twice (or thrice?) because of this. Seriously reconsidering Shopify as our platform as it seems to keep happening.
Edit: BTW, a good idea is to make backups. Both of your products (export products to .csv) and of your store front code.