500 Internal Server Error after updating

Hallo. I installed a new plugin (Polylang) and then updated WP to the 3.4.2 version. This is the result:

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Internal Server Error

The server encountered an internal error or misconfiguration and was unable to complete your request.

Please contact the server administrator at [email protected] to inform them of the time this error occurred, and the actions you performed just before this error.

More information about this error may be available in the server error log.
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I cannot access to the control panel, so i really don’t know how to fix errors or delete plugins…