Fabiána,
For recovering documents after a crash, see here and here,
https://helpx.adobe.com/illustrator/using/whats-new.html#recovery
https://helpx.adobe.com/illustrator/using/crash-file-data-recovery.html
As it appears, if there is something to recover, you will know when starting up. Proceed carefully, and choose the right options, including whether to overwrite the original document or create a new one; the latter is safer: with the former, work done after the last automatic save will be lost, and an incomplete recovery may have be worse than what you had.
And if you have a CC subscription, saving files in your Creative Cloud Files folder will automatically create and keep versions up to 10 days.
One thing often tried first is to create a new document and File>Place the (PDF contents, if any, of the) corrupted one to see how much may be rescued that way.
Here are some websites where you can see whether it can rescue the actual file, and if it can, you may pay for a subscription to have it done,
http://www.recoverytoolbox.com/buy_illustrator.html
http://markzware.com/adobe-software/fix-illustrator-file-unknown-error-occurred-pdf2dtp-file-recovery/
http://www.illustrator.fixtoolbox.com/
http://www.erepairillustrator.com/
As far as I remember, the first one is for Win and the second one is for Mac, while the third and fourth one should be for both.
Here are a few pages about struggling with it yourself:
http://daxxter.wordpress.com/2009/04/16/how-to-recover-a-corrupted-illustrator-ai-file/
http://helpx.adobe.com/illustrator/kb/troubleshoot-damaged-illustrator-files.html
http://kb2.adobe.com/cps/500/cpsid_50032.html
http://kb2.adobe.com/cps/500/cpsid_50031.html
http://helpx.adobe.com/illustrator/kb/enable-content-recovery-mode-illustrator.html
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