Any reinstall of a single-use EULA Windows on a new device will trigger re-activation.
If you activate the new copy within the 30 day trial, the old version automatically becomes invalid (a "pirate" copy, no longer legally usable).
The EULA does not allow two working, legal copies of the same OS.
Decide which one you want and activate it from control panel > system.
Activation should get automatic validation, but if not, just phone the free MS number and ask for a manual validation key. Explain that you've moved the OS to new hardware.
(btw If it's an OEM copy of the OS, you can't move it to new hardware, though they'll normally accept a HDD replacement provided that the mobo, graphics etc are unchanged)
