What does this message mean when you boot your computer (Disk boot failure Insert system disk and press Enter) ماذا تعني هذه الرسالة عند اقلاع الكمبيوتر?

When starting the computer system, a 'disk boot failure - insert system disk' error can occur for several reasons, including either hardware or software changes. It may also occur if there is a CD or a diskette in the drive while starting the computer. An incorrect boot sequence, a newly installed hard drive, an unplugged hard drive or a damaged disk may result in the the disk boot failure insert system disk error

The PC's Boot Order may be Its Selected CD ROM or HDD is Not detected Otherwise hard disk Dont have OS 

the bootable dish(hard disk Drive) are not shown on boot sequence

It means that the computer didn't recognise any bootable disk in the computer.

Press F2 OR Del Key, Open BIOS Check First Boot Device Priority, If you found first boot is HDD, Power Off your computer and Re-Connect HDD Power Connect and Data Cable.

Try to reconnect your hard drive if it is detecting in bios then you need to format your hard disk using diskpart 

if your disk working then check the mbr boot if you dont want install new windows 

and the grub in linux