Follow up to this thread,
http://forumserver.twoplustwo.com/48/computer-technical-help/laptop-wont-boot-cant-reinstall-windows-discs-wont-load-1217653/#post33598959

I decided to get a new hard drive. In Windows diagnostics somewhere it shows I have a 250GB hard drive so I know it's installed correctly because prior to this it showed my old hard drive which was 166GB.

I try installing the old drivers which includes Win XP. I tried installing win 7 and no hard drive shows up

Yesterday on my old hard drive it said something about bootmgr missing

Today on the new hard drive it blinks and says no array defined.

What do I do?

I have three options in the boot sequence. One is USB storage device. Second is diskette drive on board NIC, third is CD/DVD/CD-rw... I could have swore I had 4 options yesterday

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.