Praise be to Allah.
There is nothing wrong with taking part in competitions held on the internet or elsewhere, if the entrants will not lose anything and they will either be safe and sound or will win something, because that does not involve gambling. Gambling means that the person does not know whether he will gain something or lose something. But this is subject to the condition that the competitions are not contaminated with haraam things, such as questions about permissive things or songs, or other things that are forbidden in and of themselves. Then they would be forbidden for this reason, not because they involve gambling. And Allaah knows best.