Kewin888, thank you for the treat to 2 very ‘charming’ videos @youtube. That has delayed this response.
And Two languages are to your credit. Obviously we are losing a bit in the translation.
Your problem falls between ‘networking’ and ‘security/web’.
No logs --- infection - not assessed
For the differences between computers, this tends to suggest firewall settings differences.
Firewalls can target specific sites / URLs.. Check the logs.
Differences between ‘spyware killers’ protecting the computer can refuse loading pages because part of the content is coming from a ‘forbidden advert’ provider.
And yes, the browser has security settings.
You can briefly lower the security protections (step-by-step) to help localize the problem.
The command prompt (start > run > cmd) makes some commands available to you.
The firewall controls at all levels. CMD level avoids browser security & most spykillers.
Sample commands (networking forum has more info)
No DNS involvment
tracert 208.117.236.72
tracert 208.65.153.238
DNS involvment
tracert
www.youtube.com
tracert nz.youtube.com
There will be differences. Youtube has many mirror sites. Time-of-day can vary the routes.