you may have a old manual which your dealer should have updated. I was in the same position
instructions are here. Covers everything you need to know
http://www.350z-uk.com/forum/viewtopic.php?t=2713
it's the laser thats going. Had it happen in the TT which was bose also. Luckily in the TT the CD was a separate unit and Audi would do a recon exchange for £90. Don't know if Nissan will do the same seeing as some cars are now out of warranty.
BT kit has only been out for six months so if the previous owner had wanted a blue tooth kit, then it will be a aftermarket one. Try 0000 or 1234 as a security code. Tends to be the norm
I'd just like to wish you all a Merry Christmas and hope you a have a good New Year.
Here's looking forward to continuing to make this the best 350z Forum.