Firstly I badked up my HDD to an external hard drive before I tried to do a data migration to move my OS from my HDD to my SSD otherwise it will be in my pc not being used, but because there was too much on my HDD to migrate everything I have to delete everything but the OS witch I didn't mind doing as I've got all my files on the external HDD, but some how along the way I think my OS files got courupt, well I get a blue screen when I boot up my pc and it says missing files, before all this I upgraded to windows 10 not sure if that will make a difference, but when I now put in my windows 8.1 disk and try to install I won't work, so I tried to factory reset everything that didn't work because of missing files and I don't know what to do, farther isn't happy all that money wasted and I really need some help. Shall I try to format my HDD and SSD from the CMD then try to install windows again?