is something on my computer blocking access to some sites?

[Crystaltipsandalaistar]

I can't get on youtube, all of a sudden, it keeps saying I need to download a new media player, which makes no difference. Also I am trying to get on the walker crisp site to do the competion and it says 'done' but it's empty. There is an error message thatb says 'problems with this web page may stop it being displayed or functioning properly. and then it mentions error - object required. i have no idea what has suddenly changed since yesterday