Disk Boot Failure. I left my computer on for a while, when i returned to it, the screen was black

Question

I left my computer on for a while, when i returned to it, the screen was black and nothing was seen even when i moved the mouse. So i switched off the power to the computer and let it rest for a while.

My computer is a acer aspire X3600
Later, when i turned it on again, the computer started up and then the screen remained at this:

verifying DMI pool data.......
boot from AHCI CD-ROM:
diskboot failure, insert system disk and press enter.

what can i do to get my computer to start up again, URGENT! DEPSERATELY NEED HELP!

thanks.