How can I find my Microsoft office product key?

I went through about 2 or 3 PC's...(by the way, Toshiba SUCKS! Don't ever buy one.) Anyway, I brought 2-3 computers and they all crashed for one reason or another. but this was about maybe 10+ years ago. I computers were Office came on the computer and once I actually bought a product key. I can't find it, but I have my old computers and just the box where my office product key came in. I have absolutely no idea where it is, especially after moving. Anybody have any ideas on how to get it? I called support, but they sad without the email I used, there is no way to pull it up.