Can't get past message "reboot and select proper boot device or Insert boot med

when I turn on my computer it shows a black screen with the message "reboot and select proper boot device or Insert boot media in selecccted boot device and press a key". I reboot the computer and the same message comes up. using the F8 key does nothing. I even tried other F keys but no results. How can I get past this problem?

if that doesnt work, check that the power / ide /sata cables havnt come loose inside the computer

and if that doesn work try a boot rescue cd like hirens ultimate boot disk

and if that doesnt work try reinstalling windows

and if that doesnt work, cry and buy a new hdd