last year I format my computer and put windows 8 64bit oem which I own. everything was great. then I upgraded to 8.1 through the store. no problems. for the last few days I have been having problems with virus. so I decided to reformat and reinstall windows 8. this is what I get. windows cannot be installed to this disk. the selected disk has an mbr partition table. on efi systems, windows can only be installed to gpt disks. what happen. and what can I do to fix this.