I have a WD 750GB HDD (7500AAKS). Just yesterday, it started behaving waywardly. The 'symptoms' are as follows:
In the detecting peripherals stage during bootup where it detects the SATA and IDE devices, it would hang every now and then for a while before moving forward. And yeah then it won't detect this HDD. Now I know this could be a PSU issue too, but the strange thing is that in front of the SATA port that I would connect this HDD to, it wouldn't say "not connected" etc, just would leave it blank. That is, every other SATA (and IDE for that matter) port would have either the device name (my DVD burner, other HDD) would appear or "not connected", while the SATA port (I have tried switching ports) before which this HDD would be connected would have nothing written before it.
Second symptom is that while working in windows, it would simply hang. The mouse would move, NUM Lock works (LED blinks on and off), but nothing responds.
Here are my system specs:
Core i7 920
Foxconn BloodRage (Bios P07)
Corsair 6GB DDR3 1600MHz Dominator
CoolerMaster Real Power Pro 1000W
Cooler Master Cosmos 1000
ATi X2600XT 256MB, just one GPU
WD 750 GB
Test the HDD in another PC... If the other PC doesn't recognize it, then you should RMA. If you don't have another PC to test on, disconnect all the other IDE/SATA drives, and test the 750GB alone. Try it on different SATA ports and even try to a different SATA cable (if you already have another SATA drive which you know works, use that cable instead and use that SATA port). It's important that the SATA cable is not loose, my SATA connection cracked one day on my Raptor 150GB, and the drive would and wouldn't work depending on how the cable was positioned. If you test it out and the HDD works fine, then it's some sort of setting in the BIOS screwing up. I can't think of what exactly, but it should be in the Boot priority, RAID, or drive sections. My Corsair HX1000W is being RMA'd, so I can't give you any general description of what to look for in the BIOS.
By the way, I have a Cosmos 1000 myself. Best looking case ever made.