Windows 8

Please i bought a system that has windows 8 as the original operating system..but since i don't like the operating system and want to downgrade to windows 7...i ran windows 7 installation in a flash drive but it refused installing..i had to go buy the windows cd..but still it still doesn't work..when i enter windows setup..the reply i get is that a required file is missing or contains error..the file name is

File:\$WINDOWS.~BT\Windows\system32\winload.efi

Status: 0xc000000f



please i need help to fix this as sson as possible