You are allowed only 2 active installations. The install on the crashed drive is considered active. If this is a problems you need to call Adobe and ask for a reset.
If asked to a qualifying product when instlling CS6 type in the s/n of Cs5.
Do you have the s/n of CS6? If you registered CS6 you can go to Adobe and click on My Products. Should find s/n and download link here. But word to wise. Burn the download files to DVD and save in safe place with s,/n in case you have problem in future.