The simplest solution is that your system is booting from the wring drive. Press F8 at the first BIOS screen and you should get a boot menu; select the correct drive and see if it boots. If the problem was as simple as having the wrong boot order, you fix boot order in the BIOS and all is well.
For any solution after this, use another computer to make a copy of the drive first!
If you have real OS installation dvds (what version are you running), you can boot from the installation disc and choose a Repair installation. This will frequently fix a damaged OS install.
Worst case: Buy a new drive (or take one out of a drawer), make it the only drive connected to said machine, re-install the OS, and copy the files that you need from the drive that no longer boots.
Let us know what you try and how it goes.
Sorry for replying so late... I was really busy receiving all my boxing day orders :P. I contacted dell for them to send me a windows 7 cd to try what they told me to do. They said before they send it, they wanna try fix the problem. They told me to do a NUMBER of things. They finally told me to press f2 on start up and select diagnostics... that fixed the problem. Thanks for your help.