blocked user on my installation

Hi, I’m quite new to wp so highly detailed responses aren’t going to be of much use.
I installed bbpres and bbPress WP Tweaks. I added the widget for login / lost password etc and all worked well – for a couple of hours.
To test the site I had logged in as a guest through a different browser.
I added text to the homepage as admin then viewed it as user. All ok.
I then tried to drag a short video clip into the comment form of a forum as a user – I don’t know if this is allowed but I tried it anyway.
Next thing I know is that I get a new page with nothing on it except the word ‘blocked’ in the top lh corner.
I closed the browser, re-opened it and tried again. Still the same.
As admin, I couldn’t get into the system either. I had to go to the control panel and get in through there, I do have access as admin now though.
I still couldn”t get access as a user, so I tried removing and reinstalling the widgets and the plugins, bbut still can’t get in as a user even though the user account exists.
Anyone else had this problem and how do I fix it?