computer problem....please help!!!!

getting a black screen with the following message....
boot device not found
please install an operating system on your hard disk
hard disk (3FO)

f2 system diagnostics.

I have ran the system diagnostic... start up test, run in test. no issues there. hard disk test says hard disk not exist.

don't know how this happened or how to fix it.

Presario cq57 339wm. windows 7 home premium.