Hello there, it sounds as if the PC is having problems booting from your hard drive, or is trying to boot from somewhere else (Disk/External device)
Pop over into BIOS and just check that the hard drive is being detected. If it is, you may need to modify the boot order so that the hard drive has first priority, so the computer knows to boot from it.
Check there are no discs in the disc drive and make sure you don't have any external devices plugged in that have their own memory. (printers/usb sticks etc) This is because sometimes the computer can try (and fail) to boot from these devices.
If this fails, have a go at disabling PXE boot from the BIOS menu, as your computer may be trying to boot from your network.