2nd Hard Drive not showing up

My 2nd hard drive which I store all my media on is no longer accessible. About a week ago I started up my PC, which is attached to my TV, and my Avast antivirus popped up with warnings about a bunch of viruses. I posted in the Security/Malware forums for help, but have not received any yet. I also lost access to my 2nd hard drive where my media is stored, so I am unsure if they are related.

It was showing up in My Computer and my Device Manager, just not accessible. Every time I would try open it I would get an I/O device error message. Today is the first time it is not even showing up in My Computer or Device Manager.

I'm a computer noob and do not know how to approach this problem. I am good at following directions and Google, and is the only reason I was able to install the 2nd HDD on my own.

Where do I start? Is there anything that I can do? I would really like to salvage the data on the HDD if it is possible.

It is a Seagate Barracuda ST315005N4A1AS-RK SATA 3Gb/s 1.5TB 5900RPM 32MB Cache.

Here is my PC info:
Microsoft Windows XP, MCE, Ver. 2002, SP3
Intel Pentium 4 CPU 3.40GHz
ABIT AA8 DuraMAX motherboard

2.00GB of RAM, 4x Corsair Value Select 512MB PC2-2400 DDR2 SDRAM
Seagate Barracuda ST3120827AS SATA1.5Gb/s 120GB 7200RPM 8MB Cache
Seagate Barracuda ST315005N4A1AS-RK SATA 3Gb/s 1.5TB 5900RPM 32MB Cache
ATI RADEON X800 XL 400MHz 256MB
L&C LC-B450E 115/230V 450W 60/50Hz

Thanks for any help in advance!