Site crashed after innstalling WPMU recomended plugin

My multisite crashed when I installed a plugin recomended in your last newsletter "25 Must-Have Plugins for WordPress Multisite Networks." I installed the plugin "W3 Total Cache", and my site crashed. I got a "500 Internat Server Error".

Deleted the plugin via FTM, but still the same problem.

Please help!

Regards

Benny