Error loading operating system for latitude d600

boot it from whether usb or cd drive then format the os in which it is previously installed or if ur problem doesn't end here then disable ur SATA drive to ATA then restart ur PC to check OS has booted

try to use another windows cd in case of a restore that is located in the internal hard drive and in the restore process it will show a problem and dont complete the restore that have two possible causes one bad hard drive second bad restore partition on restore whid virus in that case you need to restore from a original cd thanks and hope i was good help