Okay. After reading through this thread and banging my head into my keyboard over some of the suggestions. Oh, tommy... hitting my keyboard didn't cause my hard drive to crash. If that happened to you, it was purely coincidental.
Now, onto the problem. Please forgive me if I'm talking to you like you're stupid or something, because I'm really not. I just don't know your level of computer hardware knowledge.
It sounds as though your hard drive is failing, or has completely failed already. When the computer boots up, do you see an eMachines logo? Or do you see something like this:
If you see what's on the image, look at the Primary Master and see if there's anything there at all. If there isn't, either the hard drive is toast, or the cable has been disconnected. If you can't see that screen, go into the BIOS, and look around until you find the spot that would list the primary master and slave. I couldn't tell you exactly where it is, since every BIOS is different.
To check if the cable is disconnected, you'll need to open up the case of the computer. You're looking for something that looks like this.
It will have one of these two types of connectors.
Unplug and plug back in both of the connectors from the drive. Then, follow the data cable (the wide flat one if it's like the one on the left, or the smaller thin one if it's like the one on the right), all the way back to the motherboard. Unplug it and plug it back into the same port it was on.
If that doesn't work, then that tells me that there is something wrong with the drive itself. You can further determine this by getting a diagnostic utility from the drive manufacturer. You can find out the manufacturer of the drive by looking at the top of it. Chances are it's a Maxtor, Western Digital, Seagate, or Samsung. You may need to do this from a different computer, as I'm not sure what the capabilities are of a live OS, it's been so long since I've used one. Once you have the utility (it'll generally either go on a floppy disk (if you have one) or onto a bootable CD-ROM. All of the instructions should be there on their website to tell you what to do.
Chances are if you've gotten this far and it isn't working, the drive is toast, and the diagnostic will let you know. If that is indeed the case, then I'd recommend buying a new hard drive... they're honestly not all that expensive these days. If the diagnostic says that there's nothing wrong with the hard drive, then it could be an issue with the cable (you can buy a new one online, or from Best Buy etc), or the motherboard itself. If it's the motherboard, well... you could see if you could get someone to replace it for you, but chances are the costs would be at or around the cost of a whole new computer.
Hope this helps you out some.