Windows 7: Reboot or select proper boot device. Strange

My computer has been freezing quite a bit lately and when I reboot the gadgets on the startup screen are futher in to allow for smaller screen resolution so I assumed it was because I still have an old radeon x1900 in a newer pc and it was failing. However yesterday while playing CSS my pc lagged (felt like server but wasnt) for the first time then froze and on reboot prompted me with "Reboot or select proper boot device". It scared the shit outa me and I thought "oh no, all over" so didnt attempt another reboot yesterday ut turned her on this morning and all good for now, help would be appreciated asap. Thanks, Corey