The forum software behaves in a slightly different way to vBulletin (as found on several other forums) when entering a hyperlink.
If you select some text and click the Insert Hyperlink button
it surrounds the selected text with the necessary tags, but does not insert the actual link. The tags look like this[url][/url]
Assuming you have the link on your clipboard, press cursor left once to position the cursor between the letters
url and the first ], type an "=" and paste the link.
The link will appear
like this and will open in a new browser window or tab by default.