Help? Invalid System Disk

[caltraskoo]

So I built my computer and it is running fine, today, when I turn it on, at the BIOS, it says Invalid System Disk, please Replace System DIsk and press a key. Nothing works, I restart the computer, I replug in the plugs conencting to Hard Drive, and what not, whats going on? I went to the BIOS and told it to boot on the Hard Drive, nothing's working, WHAT IS GOING ON?

 

[leftcoasttech]

to clear the obvious out of the way, no CDs, floppy disks or thumbdrives?

 

[caltraskoo]

Thanks, I had a flash drive in the back that I forgot, this happened to me once on my XP computer too, however error message wasn't as panicky and SATA worked for booting. IDK, but Thanks a bunch