iMac is crashing at start up

I have been using iMac and I never had any issues with the same by now but then I don’t know what has went wrong with it suddenly and this morning when I switched the machine off and since then it is not starting and when I am trying to boot it up then it is automatically going in to the boot mode and at this time the bar moves across the screen and after that it stops and then shuts down, I have tried out the trick of holding down 'c' and 'd' several times but then it did not helped as well, I was able to reach the desktop and was able to manage the run disk utility once but then it said that there was not problem as such, later after rebooting the machine it started going in to the boot mode automatically once again, I had managed to run Techtool deluxe that I had got with the Apple Extended Warranty but then it was not compatible with OSX Lion because of which I was not able to run the same properly, I have also tried out command-R scenario but then it does not seems to be reloading Lion OSX, as far as I remember I was having Acrobat and Photoshop along with iTunes and Mail when I had turned off the machine last time, so I just wanted to know that are there any possibilities of them to be causing such issues, I had also installed the latest version of Skype and I did not had any issues with the installation of it so I am not able to track out the cause of this sudden issue, is there any solution that I can try out to solve this ??? Is there anyone who can suggest me some effective solutions??

In that case first of all I will like to suggest you to back up all the possible data and after that try booting from the recovery partition and you can do that by using the key combination command-R at the startup chime, when you get a gray screen with a spinning dial then release those buttons and when the Recovery desktop appear then you can proceed reinstalling the Mac OS, I will like to add here that you won’t have to erase the boot volume and there are possibilities that you won’t have to use the back up as well until something goes wrong, I have suggested you to take the back up for the safety purpose, I also wanted to know that was your Mac shipped with Lion or something else?? I am asking so because if you lion might have not been shipped with Lion then you will need Apple ID and password for carrying out the upgrade, so better check that out as well, just try out the solution that I have suggested and then let me know the response you get for the same. Hope that helps.

I have already tried out the holding down the command-R on the boot up and I had also released the keys after getting the spinning dial, it kept spinning for approximately seconds and after that there was no entry sign and this time the spinning dial was continuing, I was aware of the solution that you have mentioned but then I had never came across the no entry sign, do you have any idea about the same?? Later after trying the same several times I was able to pass it through and it had offered me the option for reloading the Lion but then as soon as I reached the disk choice of installing OSX Lion then the recovery HD was appearing to be grayed out and it also said 'This disk is locked'. What do I have to do know, I am really running out of ideas, is there any other workaround for reinstalling the osx lion?? Or taking the back up from the mac? Any further help for the same will be highly appreciated.

There are different workaround for backing up a mac if it is not able to boot well, you will have to arrange a external hard drive to hold the backup data and then follow any of the solution that has been mentioned below:

• First boot from the recovery partition (10.7 or later) and then use a Time Machine backup volume (10.7.2 or later) and if you want then you can use installation disc (10.6.8 or earlier.) as well, when you are ready with the same then just Launch Disk Utility and then follow the instruction that has been mentioned in the below article.
• Mac OS X v10.5, v10.6: How to back up and restore your files
• Secondly if you are having a working Mac having FireWire ports just like the mac that you are having issues with then you can try to boot the non-working Mac in target disk mode and for that you will have to hold down the combination command-T at the startup chime, for carrying out this task you will have to connect both macs using FireWire cable, here the internal drive of the machine running in target mode will be mounted as external drive on the other and after that you will be able to transfer the data from that machine to the other.
• Other than this if the internal drive of the mac which with you are having the issue is user-replaceable then you can simply remove it from there and then mount it in to an external enclosure and then connect it to the other mac for transferring the data.

You may need to clean the ram where it inserts that has helped in the past.

My Macbook Pro and iMac are not having the right Firewire connections but then I have tried using a firewire 800-400 connection from a old iMac but then I don’t know why the newer iMac is just not recognizing the keyboard commands because of which I am not able to use that route, I have tried out all the possible solutions that I could have but then none of them is appearing to be helping, I have raised the same issue I some other forums as well but then I have not got any luck yet, is there any other workaround that I can try out or I should simply contact the nearest Applestore and have appointed a genius for fixing this out?? A number of other people had suggested me the same after I addressed them my issues. What do you think about the same? Do you think that I will be able to fix this out on my own with some trouble shooting??