It could be an issue with your connection. Make sure you can still access other websites normally. If you're on a Google Apps domain, the administrator of your domain may not have turned on YouTube. Learn how to add YouTube as a service.

The video-streaming platform can also ban your account if there is even a single case of severe abuse like predatory behaviour, spam, or pornography. Moreover, channels or accounts dedicated to a policy violation like hate speech, harassment, or impersonation can also get banned.