Question about hard drive failure

recently i was on my computer and i got a blue screen while running windows vista. i attempted to restart my computer but when i get to my bios screen it doesnt detect my C drive and says error loading operating system. i did another restart and checked my bios and my boot priority was changed. i used to have my hard drive as first, cd rom second, and floopy third. now it only says cd rom first and floppy second. i did a 3rd restart but this time it actually detected my hard drive and loaded up just fine. however when i'm just browsing around on the internet i noticed that sometimes my comp. would freeze quite frequently roughly every 15 mins or so anywhere from a few seconds up to a minute. a few hours later i got another blue screen and again my hard drive wasnt found. i boot up my computer and i hear an odd clicking sound. i hopped on my sister's comp and looked around the net and actually found a few websites that have audio files of common hard drive problems but none of them sound like mine.

some things i've tried are cleaning out my heat sink (which was very dirty) and i tried using different cords to connect my hard drive and neither works.

i dont quite consider myself a computer person but i do have limited knowledge of computers, common sense, and access to google. can anyone suggest some things that i could possibly do to fix my computer? or at least confirm my suspicions of hard drive failure?

no i didn't, in fact i dont even know how to do that. i can only access my bios at the moment.

the computer i'm using is an Emachines T5246
this is the hard drive that comes with it.
Western Digital 400GB SATA II (7200rpm, 8MB cache)

just fyi no i cant take it back to the store because i bought it from a friend for 150 bucks couple years back and he bought it from circuit city

Or the disk is sound and the host (so-called controller) is dead, or all cables, or the power supply, or the Bios' Prom or battery...

You may download and burn a bootable Cd of Ubuntu (or the one you prefer)
http://www.ubuntu.com
as it runs Linux independently from your Hdd, it will give clues about the rest of your computer.

WD's diagnostic tools is "Data Lifeguard Diagnostic for Dos"
http://support.wdc.com/product/download.asp?lang=en
there, choose some model and download the soft.

It runs on Win to create a diskette or a Cd you can then boot on. It doesn't rely on Windows nor on the Bios to access the Hdd and is the best test to do.