Hi there and welcome to ComputerHope,
The 404 error message is an HTTP (hypertext transportation protocol) message. This means you can connect to the server, however the server is unable to locate the page you are looking for. The big red face on the error is the way the YouTube have coded it to appear on screen.
As you have mentioned about multiple AV (anti-virus), just as a note, please don't have all of them running at the same time (ie.. at start up). The reason for this is that having multiple running consecutively means this can cause confliction between them and it can actually help viruses to gain access to your PC.
Imagine you are guarding a door with someone else and you are arguing on the best way to do it. While you are both arguing you both don't notice someone else walking past you and going through the door. This is just a simple analogy to help you understand the importance of only running one at a time.
If you have all of them installed you can disable all of them on startup; by using msconfig. Msconfig is a Microsoft configuration tool. Be careful in there if you have no experience of this tool before.
By following the instructions below it means you can use one AV for scanning then exit out of it and use another from the start bar -> all programs and then whatever AV you want to use; with no conflictions.
The way to access and use msconfig:
(Note - You can Google all entries that are listed here to make sure you are disabling the right ones. If there is anything under the manufacturing column stating that is is "unknow"... Google it; as it may be a virus. If it is then follow the same steps below to disable it from running on startup)
To access msconfig click the start button then type msconfig (Note - click the run option.. if using XP). This will bring up a dialog box. The name of the box should say System Configuration, and will appear in the top left hand corner of the box. You will see a number of tabs. Only go to the one that says "Startup". You can look at the others but please don't touch them as you could do serious damage if you don't know how to use them properly.
When you are on the Startup tab you will see a list of programs that start when your OS (operating system) starts up. You will see a tick in the boxes on the left for programs that start when the OS starts up. Look for all of your AV's and disable them by clicking on the tick to make the tick disappear (Note - THIS WON'T UNINSTALL THEM; so don't worry. Doing This will also speed up your computer
).
Keep one of them running on startup (your preference as to which one starts on startup).
After doing all this you will be asked to restart your computer; so make sure you save all your work if you have anything opened then close them and restart the computer.
Once the computer restarts another dialog box will appear. In the top left of the box the name of it will read "System Configuration Utility". Click the box that says "Don't show this message or launch the System Configuration Utility when Windows start:" then click on the "OK" button. You are now finished with that process.
Run a scan with your AV and see if anything comes up.
I hope this helps you out. If anything it gives you a little more technical info on how to configure your startup process... and might also help protect against viruses. Let me know how you get on.
Regards,
Base2
