Old HD in New Tower

I inherited a G5 from my work because we upgraded. It, of course died, so I stuck my hard drives in a similar tower and now my FCP wants a serial..I put in the one that I had with no luck...now before I get chided for receiving a copy of FCP unlawfully, I got it from work so I could do work from home. However, somewhere in the last few years the stickers with the serial got misplaced ( yes I realize they should have been put in a safe place, but the horse is out of the barn, etc.) I'll probably end up calling Apple for new ones but I was wondering if there was a quick fix. This is an upgrade from Final Cut Pro to Final Cut Studio HD.