Why Youtube doesn't work with any browser?

I'm here to pray for an help, dear members of the forum...

From 20 days ago I started to have problems to see videos on youtube...

Here the symptoms:

- I can see the 30% of the videos on youtube without problems, full hd and quickly

- I can see all the videos on other websites

- I CAN'T SEE the 70% of videos on youtube... they don't start also to charge! Only black screen!!!

For example, this is a video I uploaded by myself but I never was able to watch: http://www.youtube.com/watch?v=84yM1aPqiZI

A friend of mine come to my home, and using his pc he was able to watch it without problems (using my same wi-fi connection).

- I CAN'T SEE these videos using Internet Explorer, Mozilla or Chrome... they do all the same thing: black screen!

What I did:

- I deleted Mozilla and Chrome and I restored the previous version of Internet Explorer

- I unistalled Java and Flash Player (completely) and all the things related

- I reinstalled the browsers and when they asked me to install flash player to watch the videos I installed the last version of Flash Player (for IE and also for others).

- I read this post: http://forums.adobe.com/message/5802490#5802490

   So then I deleted Flash Player again and I tried to do all the things suggested in it... but nothing is still working... black screen as  always!!

What happened before:

- I installed Mozilla Firefox for the first time, just to see how it works

- I installed a trial version of Adobe After Effects

(Then, thought that one of them could made this proble I deleted both, so now they are not on my pc).

- Maybe Flash Player, Java and Windows updated their things... but I have no idea of what they did.

My System (Samsung Laptop):

- Windows t Home Premium (64-bit)
- 4 GB of RAM
- CPU Intel i5- 2450m 2.50 GHz

- Integrated Intel VGA
- nVidia Ge Force GT 520mx (with last drivers)

- Flash Player 32-bit:  Activex and Plug-In  version  11.9.900.117

- Internet Explorer 11 and Chrome (last version)
- Java 7 Update 45 (reinstalled today)

I really hope someone could help me, I'm really so frustrated of this situation