Cannot format 500gb drive

I have a pair of WDC WD5000AAKS 500gb drives that I have been using for over a year at least. Recently tho, I had a problem with one of them that caused me to loose my OS, and now that disk will not format any more.

I used the Lifeguard Diagnostics, and it passed the SMART test, the quick test and the extended test with no problems.

I also tried the Write Zeros option to try and ensure it was blanked out - then tried a full format (in Win 7), and after an hour of formatting it gave me a message to say it couldn’t do it.

I have also tried formatting it using a XP install disk, and also a Linux install disk - same result.

My main OS is Win7 Pro - and mobo is an ASUS M4N82 Deluxe - Nforce 980a SLI chipset

Does anyone have any suggestions what to try next?

The drive is still under limited warranty.