The system is trying to boot from a network device. Tap F12 at boot and run full diagnostics to be sure that the hard drive/SSD is detected and functioning properly. It could be a drive problem. If that looks good then reboot and tap F2. Make sure that the boot order lists Windows Boot Manager as the first choice. This forum post has more information.

Try disable PXE in bios.

how to enter bios as already described in 1st reply

1. Turn on (or restart) your computer.
2. During POST, when the DELL logo is displayed, watch for the F2 prompt to appear, and then press F2 immediately.