iMac Startup and New HDD Install Issues...

I am attempting to repair a newer iMac for someone and it's acting very strange. They initially brought it to my attention because it would not boot properly. Upon startup, the machine would just sit at the grey apple screen with the spinning wheel and never move. It will not boot to Apple Hardware Test, OS X Recovery System, Startup from a disc or USB, or even do anything in target disk mode when I hook it up to a MacBook. Soooo I went and bought a brand new WD 1TB HDD and stuck it in there. I plug into a working ethernet and when I attempt to do a NetBoot Recovery I get a blinking globe for about 5-10 seconds and then it attempts to boot from the new (blank) HDD at which point it gives me the file folder with a question mark on it. I even tried booting from a retail copy of OS X Leopard v10.5.4 (which I've read won't even work for this application because this iMac is too new?) and all the machine will do after I insert the disc is continuously reboot itself every 3-5 minutes... The moment I take the disc out, it stops rebooting. Pretty stumped on this one. The inability to do any kind of hardware testing is not helping in the slightest so any insight or idea ya'll might have would be greatly appreciated.
Thank you,
T

Alas Apple has made 2010 and later iMacs with a propritory hard drive and sensors and generally only use Seagate drives. Might be better to take it back to Apple if it has AppleCare 3 year warranty but if you opened it that may be voided. Read this:-


http://blog.macsales.com/16878-imac-hard-drive-upgradeability-expanded