SOLVED! Seems really random but I found a suggestion on Reddit to run windows memory diagnostic tool and now it's showing up and have been able to format it.
I've just installed a second SSD (Samsung 2TB 980 Pro PCIe 4 NMVe M.2) into SSD slot 2 on my Alienware m17 r4 but it is not being recognized by Windows in either file explorer or disk management.  However, it does show up in Bios (see photo). I haven't changed anything in the bios since purchase and it shows the boot list option as 'UEFI'.  I've read a couple of other articles on here about activating the SSD inside bios or even changing the boot method but I'm not a technical man so it's all very confusing.  I'm wondering if it has anything to do with the SSD being PCIe 4 (as opposed to 3). I ran a Crucial system check and they recommended their own gen 4 so I thought it would be compatible. [IMAGE][IMAGE][IMAGE][IMAGE] Any advice would be muchly appreciated!
m17 R4, not recognizing second SSD