When this has happened to me, I've put my ear on the case of the laptop when I powered on, to see if the drive was still spooling up.. Sounds simple, but this may tell you if the drive is just flat-out dead or just not registering.
If you have an emergency boot disc (floppy, or OS CDROM, or Recovery disc from Dell) I'd through that in the drive to see if it will boot to that. If you can get it to boot using one of these discs, try to run scan disk. I've actually gotten a machine to come back to booting up with that method- I used automatic fix mode for any problems identified, and I guess I got lucky..
Another technique is to find a friend who is super nerdy- they just might have a "Knoppix" bootable Linux CDROM and a memory flash drive. If that is the case, see if they can't boot your laptop in Linux, mount both your hard drive and the memory drive, and save some of your files, etc.
Good luck!