Update: 9/21/2018 - In preparation for Open Beta, all real money transactions have been disabled.
There's currently a known issue in which in rare circumstances the store can appear disabled when you log in. If you see this, first restart your client to see if that resolves the issue.
If the store is still disabled after a client restart, check the Server Status thread in the forums to see if we are having an outage.
If you continue to have problems accessing the store, use the Submit a Request link in the upper right of this page to contact customer service.