Re: installed new hard drive on my laptop but it isn't recognized. please help. frustrati
try re-seating the hard drive. if you're sure the new drive works fine (check it in another computer?) then at this point i'd have to say that you should (imo) just take it to a repair shop. if it's not recognizing that you have a hard drive attached at all now then it's possible that there are things wrong that you couldn't diagnose/fix yourself.
edit: try using a live CD to run tests first. check dell(?) to see if they have a bootable CD to run diagnostics on the hardware. if nothing else you could just use a ubuntu live CD just to see if everything else appears to work besides your hard drive.