how to make links in "Blocks" not to open in a new window, instead to open in the same window?

Edit the Block template's href code in System Admin->templates->[moduleName]->[BlockName.html]

Most links not related to XOOPS core will open in a new window.

hum the block isnt there, it's a custom one..

I didn't realise it was a custom block, thanks for the clarification. If you had mentioned that one detail I would have explained myself better.

Just use: target="_parent">Link text in your custom block. If it is just a plain html page, that's all they will see, essentially taking the user outside of XOOPS.

By default, links open in a new window, unless it's coded into a module. The only way to get them to open in a parent page in XOOPS is modularize your pages like other modules, or create custom pages with XOOPS includes (see below)

include('mainfile.php');
include('header.php');
$xoopsOption['show_rblock'] = 1;
?>

Your Content

include('footer.php');
?>

Im not 100% sure, but it may be possible to just change your custom block to php for internal links, but the pages you are linking too will still need to be saved as .php and have the above mentioned code included, otherwise the page will just display as normal without XOOPS "wrapped" around your custom content.

sorry for not mentioning it's a custom block, it works fine now thanks