Problem with checkout

I've a strange problem and I'm not able to solve it. On checkout, at the step "shipping" I can choose shipping option. But instead the forward button I see only the "Back" button. The checkout process  stucks  at this point. But all configured in the right manner. Anyone any idea? Tried already so many things, but nothing helped.

re:   "Back" button

Normally, Back is not a "button", but rather it is an anchor (<a href....>).
The Continue is a button.

So, maybe you customized the page or the CSS?  In the browser, right-click the Back, and Inspect it.   Normally, the enclosing div looks like this

<div class="buttons" id="shipping-method-buttons-container">
    <p class="back-link">
        <a href="#" onclick="return Checkout.back(),!1">
            <small>«</small>
            Back
        </a>
    </p>
    <button type="button" class="button-1 shipping-method-next-step-button" onclick="ShippingMethod.save()">Continue</button>
    <span id="shipping-method-please-wait" class="please-wait" style="display:none">Loading next step...</span>
</div>

You're absolutely right!

display: none !important;

How the heck can happen something strange like that? I absolutely speechless, because I changed nothing. But this has to  be done manually, is this right?

Thank you very much for your great help!!

Unfortunately I must come back to this. Also after editing with custom CSS to "display:inline" at the next start of my shop it disappears again. This always changes to display:none.
There must be a reason for that! I can't figure out that. Drives me crazy.
Maybe I misunderstood something completely.

That does seem odd.  Maybe you can add  inline !important to the css class shipping-method-next-step-button

Of course!  Didn't think about that. Seems to be resolved. Hope it remains this way.
Thanks again for your great and quick help.