Could an errant flying bug be the culprit? Bugs fly in here in North Florida and change my settings all the time, I don't think that they can affect the screen during bootup to change settings in the bios, but enter setup and make sure you have the drive set to start up as a SATA and not an IDE drive. There is an option for this in the 500 series, but not sure on the 800 series. If you're not sure, then go into setup with F10 at boot up and set the whole works to default settings and try again to reboot to see what happens. Any teenaged boys at your house? If so, this could be the source of your woes. Good luck, because if this is not it, then David is right, there were some bad Seagate drives, mostly 500GB models, that had early failures in this PC.
Dave

Yup, SAMSUNG HD642JJ, I bought a second one from NewEgg at the time of purchase, it's a five star drive with a gear of the year award or two under it's belt from several different souces including votes from NewEgg customers. Buyers of this hard drive are the only ones allowed to vote, so the award means something. That's the 640GB model, I don't know what size drive you lost, but it's probably a good drive as long as it's not a Seagate. I hope you didn't sell or discard your old PC yet, or lost any files or pics saved only to the new one. You should be good with the Samsung, even with the firmware update,some of the Seagates are still failing, they just have turned into a mess of a company. Good luck with the new drive.
Dave
BTW, are you a classic '57 baby like me? Just a guess from looking at your screen name...I have 3 cats too, but they co-exist with Jack Russels and Rat Terriers out here on the hossie farm. Welcome to the forum, and the occasional nightmare that is not usually the case as an owner of a TS PC. I love mine.

I have a couple of Samsung 160GB's that are 5 years old in a RAID mirror, and have never had any problems with them. I bought them back in 2003 or 2004 when WD and IBM/Hitachi was going through a bit of technical problems that worried me away from trusting them for a while. I have no problem with Samsung, and they warrant for 3 years, and the best part is, you seldom have to use that warranty. Many of my PC repair customers who lose their HDDs get Samsung replacements through me, so rest assured, you won't have any drive failures any time soon.
Funny, I welcomed you to the forum, and you were a lurker long before I got here, so my bad, and you beat me into the world as well, I'm a November '57 baby with the smallpox vaccine scars on my left shoulder and above my left knee to prove it. I guess I must have been vaccinated twice. Go figure, I haven't ever caught the smallpox, so I guess it worked.
Dave