If you use Authorize.Net as your Settlement Agent for processing credit card orders and you are unable to get any credit card orders to process, then you may still need to active your Authorize.Net account.
The Authorize.Net account can be activated by logging in to their Authorize.net portal account. Click on the Orange Banner that shows their account is in Test Mode.
This will bring you to the Test Mode Page and you will need to slide the Test Mode Button Left to Right to turn it on to Live Mode.
If this doesn't correct the issue of if you need further assistance, you should contact Payment Processing Rep or contact Authorize.net Support at 877-447-3938 and provide your Gateway Id# for help enabling Live Mode.