Hi, and WELCOME TO TECHIMO..!
You should be able to re-install using the original media and key that you got.
You might find that it throws a message about it having been installed, but if you are re-installing it on the same physical machine, then it shouldn't be a problem. Worst case scenario, you would need to call a (freephone) telephone number for an activation/re-activation code, but that is the worst case....
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I've seen the light... It was green, flashy and attached to a Network Interface Card...
Whenever someone says "You can't miss it" I invariably do...