Reformatting.. HD not detected?

So I'm reformatting Windows XP.  And my Hard Drive isn't detected.  Here's the scoop:

Got a new PSU, plugged it in.  The 24-pin goes into the motherboard.  There's a square-ish 4-pin that I also plugged into the motherboard.  I have no idea what it does (enlighten me), but it fits there so I put it in.  I plugged a 4-pin into the CD-ROM drive.  I plugged a flat pin thingy into the Hard Drive.

From the Hard Drive, there's a smaller blue flattish thing going to the corner of the motherboard.  There's an unused space on the Hard Drive, looks like an 8-pin thingy.  No idea what should go there.

So, uhh... what am I doing wrong?

hard drive should have two thingies plugged into it.  one ribbonny thingie what plugs into the motherboard (or hd controller card which you probably don't have) and one power cabley thingie what plugs into the power supply.  these things usually only plug in one way, otherwise the red wires usually end up facing each other.

if your hard drive isn't being detected, it's possible that the cables aren't plugged in properly.  unplug and replug them in (including the end what's attached to the motherboard) and see if that helps.  ide cables are notorious for getting loose while fiddling with other stuff, at least in my experience.

also possible that the power supply itself is gummed up.  try a different power plug.

is the power supply providing enough power to run the whole system?  if it's rated for equal or higher than your old power supply, should be fine.

other than that, nothing i can think of unless you added more new hardware, blew up your BIOS settings, or your hard drive coincidently broke down at exactly the same time for no apparant reason.