Do you have another machine available to you? if so I would use that.
F12 on a dell will give you the boot menu, one option is the dell diagnostics. Error code 0142 on a Dell is a failing hard drive. At this point back up whatever you can and use dell's website to see if your PC is still under warranty. You can also call and use your express service code (all numbers so it can be used via touch tone phone) to see if you are under warranty. If you are not under warranty I would suggest a couple things. Either bring it to a repair shop where they can clone your system to a new drive and repair or do the procedure yourself. I do at least 4 of these a week and they range from difficult to VERY easy. Depending on how bad the drive is you can actually repair windows 7, just make sure you use the correct disk, ie. you have win7 pro sp1, make sure the disk is the same. Windows 7 can only be repaired if you can boot to it (they call it an upgrade for some reason). After cloning I would suggest a check disk (chdsk /r) be run to ensure consistency on the new drive, then perform a repair.
Xp was the best for repair, to bad they dropped that...