If my account was put on hold without credits, can I add credits by adding a certain number of books?

Aside from the initial "welcome" credits when you first join, you can't get any more credits just by posting books to your shelf. You'll of course get credits for sending those books to someone requesting them.  You can also buy credits from the PBS Kiosk--or from other members at a lower price--check out the threads in the book bazaar of folks selling credits.