My pc has an error of "NO BOOT DEVICE FOUND" when trying to boot.

Expounding on previous answers which have already pegged the attempt to boot from the network.

A computer typically has a list of devices it will look for operating systems on. This list is stored in order of priority. Typically your internal storage drive is fairly high in this list. But if it didn’t find your normal operating system (Windows, I assume) on that disk, it would skip to the next item.

In my recollection, PXE boot (Pre-execution environment, which is a really fancy way of saying that boot is enabled over a network rather than from an installed or physically connected disk) can be added into the boot order just like any other potential media a computer might have, so it may have launched into this, in the absence of other options.

If this is the case rather than a simple misconfiguration of boot settings, no boot device found errors usually indicate one of three things to me immediately.

The boot configuration data on your hard drive is either missing or corrupt. OR your storage drive has failed. The rare third case would be that your hard drive is reading as disconnected (either it shook loose or a cable is bad). Check to see if your drive is recognized all within BIOS. If you can confirm your specific model number we can see about finding more specific directions.