My Dell Optiplex GX150 will not reboot. I have a message saying
Secondary hard disk drive 0 not found
Secondary hard disk drive 1 not found
Strike the F1 key to continue, F2 to run the set up utility

Nothing happens when I hit the F1 key but F2 takes me to the setup utility.

Depending upon your hardware experience
You will need to remove all power (ie power cord out) and then open the side panel and reseat the Harddrive cables

Howmany internal harddrives do you have?
Are they Sata o IDE configured?

You should also run F2 into CMOS settings, and run Bios defaults

Thanks for replying Kimsland. I have one internal harddrive. And it is IDE configured. Can you give me instructions on running F2 into CMOS settings and Bios defaults plz.

In the F2 setup utility, you will need to navigate around (I believe it's Alt key plus P key, to change setup pages) until you find defaults (it may be worded slightly differently) Enable setup defaults, then save and exit (which I believe is either Esc key on its own, or F10 then Esc)