You might have a javascript error somewhere that is stopping the core from working.

You could open your browser's console (press F12 on your keyboard to open developer tools and look for the console tab) and look for errors there.

I'm having the same kind of problem. It will let me put one item (any item) into edit mode but the item shows up in html. Then the page locks up and I can't get out of edit mode. I've attached a screen shot.

I tried the F12 idea, and this is what I get:
underscore.js:1 Uncaught TypeError: Cannot read property 'replace' of undefined
at Function.x.template (http://www.yoursocialmarketingassistant.com/concrete/js/underscore.js:1:13153)
at x.(anonymous function) [as template] (http://www.yoursocialmarketingassistant.com/concrete/js/underscore.js:1:12648)
at d.Area.init (http://www.yoursocialmarketingassistant.com/concrete/js/app.js:5:17901)
at d.Area (http://www.yoursocialmarketingassistant.com/concrete/js/app.js:5:17665)
at HTMLDivElement.<anonymous> (http://www.yoursocialmarketingassistant.com/concrete/js/app.js:5:3700)
at Function.each (http://www.yoursocialmarketingassistant.com/concrete/js/jquery.js:2:2975)
at m.fn.init.each (http://www.yoursocialmarketingassistant.com/concrete/js/jquery.js:2:835)
at d.EditMode.scanBlocks (http://www.yoursocialmarketingassistant.com/concrete/js/app.js:5:3627)
at d.EditMode.init (http://www.yoursocialmarketingassistant.com/concrete/js/app.js:5:3282)
at d.EditMode (http://www.yoursocialmarketingassistant.com/concrete/js/app.js:4:28361)
jquery.js:5 [Deprecation] Synchronous XMLHttpRequest on the main thread is deprecated because of its detrimental effects to the end user's experience. For more help, checkhttp://xhr.spec.whatwg.org/.
(screen shot also attached for easier viewing.)

Any ideas on how to fix it?

The error you have confirms that a script is failing (calling underscore.js) and blocking everything.

That error, however, doesn't tell us what script it is or where to find the problem.

I'm afraid the only way would be to dive deeper into your website's code to try to figure it out.

Thank you for the information. Any ideas on how I can get it fixed? I'm not good enough to go in and fix it myself. Do you know any websites or companies that might be able to help?

If you're looking to hire someone, you can either post a job ad on the job board (https://www.concrete5.org/community/forums/jobs1/)

Or you can hire me directly if you want :)

If you want to talk about it, you can send me a private message from my profile. Go tohttps://www.concrete5.org/profile/-/view/75201/... and click on the button labeled "Send Message".

You can provide me with an email for direct communication or we can communicate entirely through Private messages whatever works best.