Link in Formula field

I'm trying to make a dynamic link in a formula field.

I have read this post forums.zoho.com/viewtopic.php?t=139273&sid=4279a2a4bcd58ae31792162a5d1d751b

After read this post and similar the way is perfectly explained.

Well, I'm going:

I make a formula field.
I put this code (very simple link to try if works):
"<a href='http://www.google.com' target='_blank'>Detalles</a>"
or
"<a href='http://www.google.com'>Detalles</a>"

In the view, in the formula column doesn't appear "Detalles" like a link name, if not that this appear:

<a href='http://www.google.com' target='_blank'>Detalles</a>

I see others applications and this works, why not in mine???? I'm crazy about this, hours and hours trying.

Thanks!

Xavi