First off, I'm assuming that you have a E520 model. 

 

Secondly, from what you have described, I'm guessing that you removed the motherboard battery overnight and re-installed it.  If so, make sure you correctly seated the battery in it's socket in respect to positive and negative.  The positive side will be facing up.  Click here for more information from your system's on-line Service Manual.

 

Thirdly, as for your SATA drive not being detected, with the machine unplugged from the wall remove the battery from the motherboard.  Then with the machine still unplugged press the On button for 30 seconds to dissipate any remaining electrical charge on the motherboard.  Then re-install the battery correctly, plug the machine back into the wall and see if it will boot normally and detect your drive. This procedure will clear the CMOS which is useful in situations where the system has hardware detection problems.  

 

P.S. in re-reading your posting I considered another possibility..... that you updated the BIOS and left the system overnight as the system didn't complete the update in a timely fashion.  If this is the problem then clearing the CMOS should resolve any conflicts between the newer BIOS version and your system's hardware.

I definitely didn't touch anything inside the computer. It's probably that other thing you said. How might I go about "clearing the CMOS"?

You can clear the CMOS is one of two ways.  The first is by removing the battery from the motherboard as I described earlier.  The second is by using a jumper on the motherboard.  Click here for your model's on-line Service Manual and the section pertaining on how to use that jumper.

 

Keep in mind that clearing the CMOS will default all your BIOS options back to their factory recommended settings.  Not really a big deal since you're probably using most of the factory settings anyways.  The defaulting will require you to re-enter the time/date, re-adjust your boot order if you have made any changes, re-adjust your power management options if you have changed them, etc.  In otherwords settings that were changed to your personal liking will have to be re-set.  If your system doesn't have a floppy drive the defaulting will turn on the floppy drive controller.  If this happens and you get a Diskette Drive error on boot up then simply go into the BIOS and turn off the option for the Diskette Drive.  The error message will be gone on the next reboot.

So I did the jumper thing and that didn't work. All the settings (Date/time, boot order, etc.) were back a to defaults so I assume it did what it was supposed to but Windows still wont boot. Could it be something where I might need to repair Windows? I don't know if I can get my hands on a Vista disc. I try using the Dell Vista update DVD but that doesn't seem to work.

After you cleared the CMOS is the hard drive being detected in the BIOS?  If not, you may have a problem with the hard drive itself.  At boot up try running the Dell Diagnostics by pressing the F12 key when the Dell logo appears.  If that works then try running the extend test on the hard drive.  If you are unable to run the Dell Diagnostics then try running the quick hard drive test by pressing the CTRL + ALT + D keys when the Dell logo appears.  This test will give a simple pass or fail for the hard drive.  Prior to running either test I would suggest reseating the drive's cables at the motherboard and on the drive.

It does appear to be detecting the hard drive now as it passed all the tests.

If the drive is now being detected in the BIOS then your problem more than likely with Windows.  Click here for a site that offers a download of a ISO file that can be used to create a Vista Recovery CD. 

So I got the .ISO, put it on a disk, and booted from the disk. It started to load but stopped when it got to a blue/green background and no menus or anything popped up. What do I do from there?

 

*EDIT* Nevermind. It just took for ever to load I guess. 

Well, the Windows recovery seems to have fixed the issue. Thanks for all the help. It is greatly appreciated.