I encountered an error in my website, http://videoof.co.uk. I have added an A record to all of my DNS servers with the IP address 184.108.40.206, but it still does not show up. Can anyone give me some guidance on what should I do in this case ?
Your DNS records are working; I can see that IP when I look up the name.
You probably tried to use that name before the DNS entry was created, and your ISP's DNS resolver has cached the non-existence of the record. Just wait awhile for that cache to expire, and you should see it.
It's normal for DNS changes to not take effect immediately, because of multiple levels of caching throughout the system.