Sounds like your partition table might be destroyed (maybe more, maybe just that and the MBR).

Just a hunch, but if you don't have a router providing a hardware firewall, or if you do but you opened something nasty in you email, or if you use Microsoft Outlook to read email (the easiest way to infect your computer) then some nasty trojan/virus/worm may have wiped out your partition table (or worse). gpart may help you recover it, but I would at least run some partition software to see what the current partition table looks like (be careful to not write any new partition table with such software, just look but do not write anything).

Of course, from what little we know it could be a complete hard disk failure (although it seems very unlikely that 2 drives failed at once). Do we even know if the hard disks are spinning? Are they identifying themselves to the BIOS? As I said, a lot to be learned before selecting a course of action.