Hi all

First of all, I'll throw up relevant specs for the machine in question:

Core2duo cpu
Intel DG33TL mobo
650 watt OCZ power supply
6 gigs ram
8800 GTS
Vista ultimate 64bit with service pack 1 installed
ESET smart security antivirus/firewall

Up until a few days ago I was running 2 seagate hard drives in my machine and 1 externally. All Seagate SATA or SATA2:

Drive 1: (internal 300 gb) Operating system, program installations etc
Drive 2: (internal 500 gb) Data storage drive
Drive 3: (external 350 gb) Temp data storage/data transfers

The 500 Gig drive I purchased and installed recently (about 3 months ago), so it is still under warranty. One morning upon powering up the PC, I got no POST on screen, but instead got a single white underscore/prompt on the top-left of screen. Tried to reset etc, powerred down, earthed system, tried again to no avail. Since there were no memory error beeps or anything, I thought there might be a problem with the motherboard/bios, or perhaps that the power supply was starting to conk out, but couldn't double check it.

I began checking the PC by elimination and did a part-by-part boot up. This included taking out all the non essential parts and reseating them. Eventually, I plugged in my 1st HDD (OS drive) and the PC booted without a problem into Vista. At first I thought the problem had been a poorly seated ram dimm or cpu or something, so I plugged my 2nd HDD in hoping to resume normal operation. When I tried to power up again, I got the same problem all over. PC won't go to POST and I cannot get to bios setup or anything. Smelling a sick HDD, I put the faulty drive into my external drive casing. While the casing powerred up, it did not show up in windows at all, and I cannot get it to show up as an external on any other PC.

Normally a crashed hard drive will at least show up in bios or as a screwed up partition or something, but this drive just refuses to even show up. I desperately need to access the work and docs on this drive and while it is still under warranty, the data is a lot more valuable to me than the drive. Clearly something has gone wrong with the drive, but I don't know enough about HDD specifics to know what it is. (PS. The 3rd drive works fine whether internally or in the external casing)

My question/s is thus: What are possible causes of this issue? Normally a broken HDD won't cause a PC to not POST? What are my options as far as data recovery or HDD repair go? Any help will be welcome.

Many thanks in advance
-Ref

PS. I just checked to see if the HDD was shorting out, but when I put it in the external HDD case and power it up, I can hear it spin up normally. Thought that might help in diagnosis.