Have many way to do that, you can go toapp\design\frontend\yourstore\2012\template\checkout\onepage\link.phtml or to your link.phtml the one what you are using. Try remove the code and see if the checkout button miss, if is missing, you are on the right place.
So, there put this code(change all):
<?php if ($this->isPossibleOnepageCheckout()):?>
<?php if(Mage::helper('checkout/cart')->getCart()->getItemsQty() >= $minimunQuantityYouWant):?>//this code is ours
<button type="button" title="<?php echo $this->__('Proceed to Checkout') ?>" class="button btn-proceed-checkout btn-checkout<?php if ($this->isDisabled()):?> no-checkout<?php endif; ?>"<?php if ($this->isDisabled()):?> disabled="disabled"<?php endif; ?> onclick="window.location='<?php echo $this->getCheckoutUrl() ?>';"><span><span><?php echo $this->__('Proceed to Checkout') ?></span></span></button>
<?php else:?>//this code is ours
Type msg here, like "You need minimum x items to finish."//this code is ours
<?php endif;?>//this code is ours
<?php endif?>
This solve your problem.