It doesn't help to say you have tried everything because we don't know what you did. You need to explain what happened, were your trying to update iTunes or something else. Also give the error message in full with the exact text.
But taking a wild stab at it first save a copy of iTunes Library.xml which is in Music\iTunes.
Then try the following which recovers a backup library made when you last updated.
It could be vey out of date if you updated a long time ago.
If that doesn't work for you, try:
Remember that if iTunes library.xml was altered by the previous step, you have you saved copy to use.