How to backup single files trough Disk Utility

might not be the most efficient way, but you can remove your internal hdd and use it as an external (putting it into some external case). and now, run any other OSX, plug in and you should see your stuff coming up. Copy and do your backup required.

Once done, re-install back to your mbp and reinstall. =)

 

If the OP has access to another Mac with a Firewire port, Target Disk Mode is the easier option.

 

It might work with a PC, if the PC has a Firewire port and is able to read HFS formatted volumes, as Target Disk Mode is just booting the Mac into an "external HDD" mode. MacDrive is a software to be able to read and write to HFS+ in Windows, the trial is fully functional for seven days.
http://www.mediafour.com/products/macdrive/

What do you mean with CMD+D? It is there for duplicating files in Finder, other than that I'm not aware of any startup relevance with that shortcut.

 

You press and hold down the T key to get into target disk mode:

Start up the target computer and immediately press and hold down the T key until the FireWire icon appears. The hard disk of the target computer should become available to the host computer and will likely appear on desktop. (If the target computer is running Mac OS X v10.4 Tiger, you can also open System Preferences, choose Startup Disk, and click Target Disk Mode. Restart the computer and it will start up in Target Disk Mode.)
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When a Mac that supports Target Disk Mode[1] is booted with the 'T' key held down, its operating system does not load. Instead, its firmware enables the computer's drives to behave as FireWire mass storage devices.
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To activate Target Disk Mode, restart your Mac and hold down the T key during reboot. The screen will turn blue with a slowly blinking yellow FireWire icon. If your Mac is a portable, a crude battery monitor will also show up when the iBook or PowerBook is running from the battery. It is advisable to run portables off AC power when using Target Disk Mode for more than a few minutes.
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collected from Target Disk Mode

 

Does that mean, you can start the Mac in TDM, connect it to a Windows PC and read the HDD's contents via Windows Explorer upon having MacDrive installed?
Your user folder is located at Macintosh HD (name of HDD or volume/partition) / Users / YOU / Desktop.

It may be, that you don't have any read rights via that Windows method though.

And what do you mean with "I couldn't find them either when i searched for them in the disk utility."? How did you start Disk Utility and how did you search with Disk Utility?

 

"I have to erase my HDD, due to a problem in the booting. It gets stuck at the grey logo screen. I´ve tried all possible solutions, but to no solution."

When you get as far as the grey screen, but can't "get beyond" it to the blue screen, it is often a sign that your login prefs file has become corrupted.

Before you get drastic, let's review what you've already done.

Have you tried booting the computer in question from a boot DVD?
What happens?
Does it boot? Or, not boot?

Can you boot into "single-user mode"?
How to do that:
1. Computer off (shut down)
2. Press power-on button
3. IMMEDIATELY hold down the key combination "command-S" and KEEP HOLDING IT DOWN
4. You will be booted into the single-user (command line) mode. Eventually, you should just wind up at a "prompt"
5. At this point it's possible to enter UNIX comands to modify/delete files. We won't get into that right yet, just want to see if you can "get things this far". If you CAN, that indicates your hardware is OK, and that your internal drive is OK, and it's a file (or files) that is preventing the login.
6. Hmmm... try typing this (without the quotation marks): "fsck -y" (note, all lowercase, and that IS a space character between the "k" and the "-"). This does a "repair disk" routine pretty much as can be done through Disk Utility. If you saw "file system modified" while running "fsck -y", REPEAT the command and let the OS "do it again". Do this until you DON'T get the "file system modified" report any more (that means the disk was ok and no further repairs are required).
7. To get out of single user mode, type "shutdown -h now" (Again, note the use of space characters)

Try a normal reboot and see what happens.
Same problems?

Someone else mentioned target disk mode.
Do you have firewire on your Mac?
If so, do you have a SECOND Mac with Firewire also, that you can connect to?