RSS dont works

It sounds like a problem of SEF. Could you deactivate the SEF temporarily on your website and try again ? Does it work with the SEF deactivated ?
Which SEF extension do you use and which version ?

Ok. Then it's really a problem with the SEF on joomla 1.7.
What is the URL of the RSS feed when the SEF is deactivated ?

Could you try to replace the code:

$link = '&format=feed&limitstart=';

by:
global $Itemid;
$menus = &JSite::getMenu();
$menu = $menus->getActive();
if(empty($menu)){
if(!empty($Itemid)){
$menus->setActive($Itemid);
$menu = $menus->getItem($Itemid);
}
}
$url_itemid = '';
if(!empty($Itemid)){
$url_itemid = '&Itemid='.(int)$Itemid;
}
$link = 'index.php?option=com_hikashop&ctrl=product&task=listing&cid='.$pageInfo->filter->cid.$url_itemid.'&format=feed&limitstart=';

in the file components/com_hikashop/views/product/view.html.php and try again ?

Both please.

It's strange that your SEFed URL is:
www.nuestrasbandasdemusica.com/tienda/type-rss.feed
It should be:
www.nuestrasbandasdemusica.com/tienda/type-rss?format=feed
I just tried on our end and that's what we have on our joomla 1.7 test website.
That URL is converted by joomla using the non SEFed URL that HikaShop gives.
Looking online for that problem, I found that thread:
community.getk2.org/forum/topics/rss-feeds-not-working-when-add
It's exactly that problem so I suppose that what they propose should fix your issue too.