2000-0142 means your hard drive bad.
Try reseating your hard drive and then rerunning Diags. If it still fails you have your self a dead hard drive.
Check to see if your system still has warranty, if it does contact Dell and they will replace it depending on your warranty. If it doesn't you will have to buy a new hard drive either from Dell or any other 3rd party vendor www.newegg.com is a safe computer hardware site. Also any local electronic stores should have them for sale.
Can check at www.dell.com/support for your system information.
enter your service tag and you should be able to see your hardware specs and warranties. Also there is a system manual that should show you step by step on how to disconnect your hard drive and...