Hey there, Olle118.
Depends on what you mean by "reset my HDD". @theyeti87 has a good point there. If you don't have a retail copy of Windows and yours is OEM (it came pre-installed to your computer), you'd have to buy the OS (operating system, which is Windows in your case) as it won't work with the new hardware.
On the other hand if you mean formatting the drive, then yes, I'd recommend that you backup any important data which you might have on that drive and after that make a fresh installation of Windows once you have built your new system.
Hope that helps. Please let me know if you have any questions whatsoever.
Boogieman_WD