Turning an All in One into a reg. Desktop?

Hello All,
I wanted some advice on my PC problem. I have a Dell XPS One 2710 bought around 2013-2014 and spent + $2600 (I know it was a rookie mistake and I spent way too much). The motherboard doesnt work and Dell said none of its vendors carries this motherboard anymore and to just scrape this PC and buy a new one (motherboard alone online costs +$800). What I wanted to do was salvage the parts and build my first computer desktop since I spent soo much money on this All in One and I can imagine it must have some pretty good parts. I wanted to build a new gaming computer with the parts but I would like some advice on which motherboard type and size should I be looking at. I dont have a case size in mind as the build will rely on the parts to determine that. But any suggestions on the type and size of a new motherboard I should be looking at and case size? I want to do built my first PC and could use any and all the advise I can get.

Ideal I would love to save the CPU, ram sticks, hard drive, and dvd drive if at all possible and if you all think i can save other parts please let me know (wlan or tv card?)


Mo- TheRookieBuyer

Ps. This is list of the parts my All in One included-dont know if it helps and can I salvage the Microsoft key already installed there?:

-3rd gen Intel Core i7-3770S processor 3.10GHz with Turbo Bost 2.0 up
-8GB Dual Channel DDR3 SDRAm at 1600MHz-2 DIMMs
-nVidia GeForce Gt 640M 2GB DD R5
-2 TB-7200RPM, SATA 3.0 Gb/s, 16 MB Cache
-Windows 8, 64-bit
-8X CD/DVD burner (DVD+/-RW)
-Power Supply 235W