How do I shorten my first post length?

https://codex.www.ads-software.com/Customizing_the_Read_More

Samboll

Thanks for this – reading through it I realise that I think that I have a problem with my wp editor. It doesn’t show anything like bold or italic etc. and when I click on the html button – all the text disappears. There is no visual wysiwyg either. I have deactivated all my plugins – to see if this is the problem – but to no avail

try upgrading to the new 2.6.3
or upload the /wp-includes folder contents again