Hard Drive Gone?????

Hello,
I've had this HDD for a few months now but suddenly today its gone missing.
Its a 500gb Seagate HDD im not sure on the exact name or part number.
Everything was working fine earlier today i was playing a game thats on that HDD (I've had the game since August) i closed the game everything was fine and then put the computer into sleep mode like i usually do when i leave the house. I go to work for 4 hours and my sister calls saying that the computer cant find "The Sims 3" which was also installed on the HDD. When i got home i went into my computer but my Media J: HDD was no longer there. I also have a 320gb which is my C: and D: drives and it still works fine. I've looked around but haven't seemed to find a solution. I've checked the cables, disk management doesn't see it, and when i go into the BIOS it says it has 0mb... I'm really hoping its not corrupt because it has all my movies and games on it.
please help if you can.

if it matters i also installed 4 updates from microsoft but thats was earlier in the day.

Also system specs:
Acer AM1100-E1203A: Computer
2gb: RAM
AMD Athlon 64x2 6000+: CPU
320gb: Factory HDD
500gb: Seagate HDD (MISSING)
Vista Home Premium SP2 32bit: OS
Nvidia Geforce 8800gt: VideoCard