An addition to Torsten's comments:
Upgrade to the latest stable version possible, and in case of doubt, stay within an LTS.
I.e.: You didnt' say which version you were using, but please, upgrade to latest Tiki 12.X LTS if possible.
And you might want to rescue any files you had customized on disk, before deleting everything.
There is a nice utility to help you doing that, not very much known, but you can reach it at:
Admin home > Tiki Cache/Sys admin > Save Directories
Additionally, if you customized any css or tpl files, you'd better copy them first to a safe place before deleting the tiki file tree. See also: