Both 380 and 390 models look exactly the same and must have the same hardware with maybe a difference in processor speed or model. So the slight difference may not be enough to cause a non-bootable system... the only inconvenience may be the legallity of the swap, but rather tan moving the HDD from the 390 to the 380, I'd suggest replacing the failed 390 hardware with the one on the 380... or to use the Product Key on the COA sticker on the case you use so not to vioate the Microsoft COA Agreement