Computer doesn't boot up, shows PXE error and/or "operating system not found", "no bootable device", "insert boot media", or other similar error

This error usually indicates a disk failure, but be sure the disk is properly attached to the system

This usually happens when the computer cannot find or communicate with the hard drive or SSD where the operating system is installed. In most cases, this indicates that the drive has failed.

Many computers are configured by default to fall back to PXE boot in the event it cannot find a drive to boot from. The idea is that if there is no hard drive with an OS installed on the computer, then the computer may be a thin client and should try to boot from the network. Except in certain business environments, there is generally no PXE server to load the operating system from, so it fails with an error.

A failed hard drive typically will not communicate with the computer, causing it to disappear from the system. Repetitive buzzing, clicking, or beeping noises are a common indication of a hard drive failure. SSDs contain no moving parts and do not make noise during operation, so you may need to enter the UEFI or BIOS setup to determine if the system detects it or if the drive has failed. See also: How do I recover lost/inaccessible data from my storage device?

This error can also occur, perhaps intermittently, if the disk is physically disconnected or poorly connected to the computer. This is probably the case if it's apparent that the drive isn't doing anything at all. Check that all cables are properly seated and reconnect them as necessary. Also, replace any damaged cables and try using other ports or cables if available.

Less commonly, an erroneous or corrupted boot configuration can cause this error

If you just installed a new operating system or have changed the OS boot configuration, and the hard drive or SSD is operating properly, you may still get this error message, but possibly preceded by a "No active partition" error.

On UEFI systems, this can happen if there is no EFI System Partition (ESP). UEFI firmware executes the bootloader from this partition to boot the operating system, so the system will not be able to boot if there is no ESP. You'll probably need to repartition the disk and reinstall the OS to fix the problem. It's also possible that the OS doesn't properly support UEFI boot; try enabling BIOS compatibility mode and see if it works.

If an ESP is, in fact, present and you get this error, this typically means that the bootloader it contains is missing or corrupt. A procedure to repair the EFI bootloader on Windows systems can be found on the Dell support website and in this answer. A summary of the steps follows:

• Boot to a Windows installation or recovery disk
• Click Repair your computer and open Command Prompt
• Use DiskPart to assign a drive letter to the ESP
• Navigate to the directory on the ESP where the bootloader should be stored (<ESP drive letter>:\EFI\Microsoft\Boot\) and run bootrec /FixBoot
• Back up or remove the old BCD, then rebuild it: bcdboot c:\Windows /l en-us /s <boot letter>: All (where <boot letter> is the drive letter of the boot volume; add /f before All if external)

If your system uses legacy BIOS firmware or is in BIOS compatibility mode (formally known as the Compatibility Support Module or CSM), this means that none of the partitions on the disk have been set as active. The BIOS can only boot from an active partition. You'll need to boot into a Linux live disc or other environment and change the settings to set an active partition; this can easily be done with most partitioning tools.

Parts of this answer were taken from a previous answer.