500 Internal server error when activate plugin

Hi there,
Disclaimer: I’m a newbie, so excuse my ignorance.

So, I installed W3, as per instructions. But on activation my site goes down with 500 internal server error.

Is there a default config setting that’s causing this?
Or plugin incompatibility?
My site URL: inspiredgifts.net

Thanks,
Athy.

https://wordpress.org/plugins/w3-total-cache/