Can you turn on the machine and as soon as you let go of the power button can you press and hold the Command+Option+P+R keys on the keyboard.
You must press this key combination before the gray screen appears.
Can you then hold the keys down until the computer restarts and you hear the startup three times and then release the keys and let me know if the machine will then boot cleanly.
If not can you try booting the machine again and this time can you hold down the Command (Apple) key along with the S key until the screen turns black and text begins to appear on the screen which is Single user Mode
In single user mode there is no graphical user interface so when the system finishes starting up a few seconds later it will wait for a typed command.
At that point can you try typing fsck -y and press enter.
The system will proceed to run a comprehensive file directory check, repairing problems it encounters. If it does find errors the it is advisable to run the program again and again until no errors are detected. Once it is finished can you then type Reboot and hit enter to restart the computer and let me know what happens.
Can you power off your machine then wait 5 seconds then power it up and immediately press and hold down the option key on the keyboard and keep it held till you hopefully come to the Apple boot menu.
You should see a picture of yoru hard drive and if you do can you click it then click the right hand arrow and see if the machine will startup.
If not let me know if you have your OSX disk for your Mac.
I would like to try verifying and repairing the disk so we can see if there is an issue with the OSX software.
Can you put the OSX disk in your machine then shut it down.
Once it is off can you then power it back up and then press and hold down the C key on your keyboard till you see the apple load wheel under the apple icon and then let go.
Your Mac should open to the installer menu and when it does can you then choose English from the menu and click the right arrow.
Next can you click the Utilities menu on the top toolbar and choose Disk Utility to open it
When it opens can you then choose the First Aid tab and select your OSX disk on the left
You should then have the option to verify disk and repair disk, If you could run a verify permissions first then run a verify disk then run a permission repair and a disk repair, If the disk repair gives you an error can you run it a second time.
Once that is done can you then restart your Mac and let me know if it will now boot cleanly and run correctly.
Have you deleted anything recently as that error usually only appears when you delete a file or all the files from the /library/receipts folder.
At this point we can try a safe boot and see if it will repair, however if that will not work our only options would be another Mac and a firewire cable or to perform an Archive and install which is where you reload the machine and choose the archive and install option so that your files are archived so you dont loose your data.
To try the safeboot can you power off the mahcine and then power it up and immediately press and hold down the Shift key and keep it held till you see the apple log with the load icon beneath it then let go and wait.
Depending on how bad the damage is a safe boot can take 30-45 minutes before it brings you to the login screen.
If you wish to try that and let me know what happens or if you prefer I can give you the instructions to perform the archive and install.
Let me know what you prefer
This may sound weird, however I had another customer a couple of nights ago that picked up a nasty Mac virus, Although they are very rare and it is usually months apart if I see them it is strange that two people have had the same type of issue in a week.
If you could try the safeboot, You may actually wish to start the safeboot running and then let it run overnight just in case then let me know back in this thread tomorrow what happened.
As to your backup is it a time machine backup?
If so it is really easy to retore them to a new machine or a newly loaded machine.
What can I say, I am a geek and proud of it.
To reach me tomorrow just open the email you should have been sent and it will have a link in it that will bring you straight back here so we can continue, either that or if you need to reach me you cna post a question for claws224 and the other experts will let me know
You should have an email of all of this, If not just come back to this page using the link in the email and it will be here for you anytime you wish to copy, print or check anything.