Reinstall Ghost 15

i bought and downloaded Ghost 15 in late 2011. I run it only on a Windows 7 Ultimate machine. In the past year I've had some issues with the PC (can't change admin) and I'm also unable to run full Ghost backups for reasons not clear. My solution: format the drive and reinstall Windows.

My question:  My purchased copy of Ghost should still be good, right?  I can reinstall it three years after purchase, right?

I should also reinstall from an .iso file?  Is that the way to go?