Based on this information alone the technician knows where the potential problems lie.
1. "No device from the boot sequence returned any sector at all"
1.1. Check the boot sequence, is it allowing the expected devices to attempt to boot?
1.2. If the expected boot device is the hard drive, and this message is appearing, is the drive functional? (This will be ascertained last)
2. "At least one device returned a sector but it did not have a valid boot signature"
2.1. Loss of a valid boot signature on the MBR will result in a complete inaccessibility to all information on the drive, but the system should boot to an alternate device with no trouble
3. "At least one hard drive returned a sector with a valid boot signature but no partition is set active"
3.1. Missing active partition in the partition tables can easily be checked by booting to an alternate device and then attempting to read the C: drive.
Therefore the order of priority on the tests is reversed and looks like this:
1. Check the boot sequence and make sure that it includes the hard drive (in newer BIOSes the hard drive can easily be removed from the boot sequence choices altogether)
2. If the boot sequence is correct, be sure it is set to boot the alternate device first (i.e. floppy diskette or bootable CD-ROM whichever you are using) and boot to the alternate device.
3. From the alternate boot disk attempt to read the C: drive with a DIR C:
3.1 DIR C: yields "Invalid drive specification" - This means that the partition tables are missing, corrupt, or incompatible if the boot disk is a form of DOS and the partitions are NTFS. In that case use NTFSDOS.EXE.
3.2 DIR C: yields "Invalid media type reading drive C:" - This means that the partition tables are recognized but the DOS boot record is missing, or corrupt. In rare cases the partition table has been "mildly corrupted" to point to the wrong starting location for the partition.
4. From the alternate boot disk attempt to read the partition tables with FDISK.EXE
4.1 FDISK yields "Error reading fixed disk" - This means that FDISK cannot make a low level BIOS call to read the MBR of the drive. The likely causes of this in order are:
4.1.1 The drive is not configured properly in the BIOS
4.1.2 The drive's cables or connections are loose/bad
4.1.3 The drive is physically malfunctioning
4.2 FDISK yields "Warning No partitions are set active..." - This means that none of the defined partitions is set active which will cause the BIOS boot strap loader error.
4.3 FDISK yields "No partitions defined" - This means that the partition table has been damaged or completely deleted.
4.4 FDISK yields defined partitions - The actual sizes of the partitions, the types, volume labels should be inspected carefully for "reasonable values" and no "funny characters" If there are unreasonable values like FDISK reports the total size of the drive as 2.1GB and the size of the C: drive as 35.6GB, or the volume label is written in smiley faces and greek letters then the partition tables are definitely corrupt. Otherwise a corrupt OS loader code could be suspected.