The "S" models are very limited on what will or won't fit. However, even the regular size models are usually limited to the model that came with the PC (some can use a Retail (non-dell) motherboard with some case modifications). Also, if a non-Dell motherboard is used the Dell supplied Windows Operating System disc will not load (it will only load on a motherboard with a Dell BIOS).
Reset the CMOS (BIOS) and see if that helps. However, if the BIOS is corrupted on a Dell motherboard the ONLY option is to replace the motherboard.
See "clearing the CMOS settings" in the manual HERE
I am not a Dell Employee
Dell forum member since 2002
Dell Inspiron 15 - 5577 Laptop
Home Built Desktop PC with ASUS ROG Z170, i7 6700K CPU
Windows 10 64 bit Pro and Windows 10 Insider Program Beta Versions. SSD drives. Cakewalk by BandLab and Studio One 4.1 Recordng Studio Software.