Have you altered the CMOS Setup at all before the format?
Missing Operating System your error occurs when the boot record signature of the master boot record does not match a certain value at a certain location. In this case, the boot sector is invalid and the computer cannot boot. This error can also occur if there is no active partition defined in the partition table.
Also message can happen when a non-bootable disk is left in drive A during startup. If you receive this error, make sure that there is no disk in drive A and restart your computer.