Sounds like either:
(A). Hardware issue (faulty memory, storage, or USB device).
(B). Software issue (kernel, device driver, or operating system).
As it has been sitting for 6 months since bought new and is being turned on for the first time, I would tend to expect (B).
It is probably running new user setup scripts and may be checking for and applying software and driver updates at the same time. This can amount to several gigabytes of data being downloaded and written, which can be quite slow over WiFi. I would place the laptop as close to the WiFi router as possible and just leave it on (overnight if necessary). Forcing a reboot can be counterproductive - it will probably have to repeat the process from the beginning at the next start.