500 internal server error after trying to install plugins

Hi there

I get this message below after trying to install plugins for sliders.
Internal Server Error

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

Please contact the server administrator, and inform them of the time the error occurred, and anything you might have done that may have caused the error.

More information about this error may be available in the server error log.

Please help
Thanks
Karolina