adding a mailinglist form

I would like to make it possible for people to subscribe to a mailinglist I set up through Mailchimp. I made a textblock in my about-section, chose to write HTML and pasted my code. But the the whole site locks up. I can see that the site understands my HTML-code because you can see it in the background, but the frame where I put the code in doesn't go away. I will try to attatch a screenshot so you might understand better. Anything you could do about it?
Many thanks!
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