iMac fails to boot up

I am having iMac at my home. Last night it failed to boot up. I tried holding the alt key and then selecting the Mac HD but still got the same problem. I even tried Boot Camp partition and booting Windows XP but it also refused to start. I tried to repair the installation with CD but it stated everything is ok. But then why it is not booting up? I got frustrated with this and installed the OS once again, now everything is ok but I have lost all of my settings. Never mind! But I want now to take the data backup. Now I want to know what should be the reason for this issue? What steps to be taken to avoid it in the near future?

This problem may occur if your hard drive is either dead or in the end stage. I would suggest you to take the backup safely before you loose everything. And also perform a regular backups most often to avoid any losses. You can also try some of the hard disk tool to repair (if possible) any such problems. Just do a google to know some of the names in this. All note the results produced by the tool to know what is the situation of your hard disk. If the value of "Reallocated Sectors" is more than 5 then the drive is on its way out. If it is in warranty period, get it replaced from the hard drive manufacture.

I have tested my hard drive with one of the utility from Internet but it says some of the sectors are faulty. Certainly this iMac hard drive is not in warranty and so I am would not be able to replace it. If my hard drive is dead then I can't afford to spend so much money on new drive. I think I have to look for cheap one at my local area with Windows 7. I am feeling too bad for iMac.

Which iMac are you having? If I am not wrong then you should be able to crack the machine and install a new hard drive from your local vendor. Another than that if you want to install a new OS on an external HD and use that as your boot drive then you can still have your iMac back.

But I don't know how to crack my iMac and it seem to me a little risky. Can you suggest me some way to do so? Maybe I can give this a try just to avoid those expenses. One more thing, I even tried upgrading the memory module and iMac was able to detect it but that doesn't solved my problem either.