If you mean a site you were banned from, it was probably an account ban. You can clear your internet cache or download CCleaner (with the two C's) and run it. If you mean a site that parental controls blocked, beg your parents to let you on!
Can u explain the question like; are u tryin to open yahoo from ur office/Homewith web browser is usingthis problem is only for u or ur Colleges/Family.which Antivirus/ Internet security software r u...