W3 Total Cache – how to get rid of

Hello,
since W3 Total Cache had no impact on my website performance,
i tried to remove it. But since uninstall, my website is messed up.

I see this error message:

“…db.php.W3 Total Cache Error: some files appear to be missing or out of place…”

but there is no such file db.php.

Also, i can’t install any plugin any more.

Please help. In particular the creators of the awesome W3 Total Cache.
Thank you.