Windows 7: Unable to connect to many websites - please help

Ok, So I've had this problem for quite a while now and have tried to solve it without asking anywhere but I'm dumbfounded on what to do next.

My computer simply will not connect to certain websites, particularly youtube.com, no matter what browser I use. I have checked the hosts file, run a malware scan, pinged youtube using DOS (and gotten a response) and taken my wireless router out of the equation, all to the same result: nothing.

If there is anything else I can do to possibly resolve this problem please assist me.

PS: I would also like to mention that I was told that this could be a problem with my ISP.
I do not believe this is the case due to every other device on my network being able to access youtube. This includes my Xbox, smartphone, iPad, and laptop, all with no problems. My main PC is the only device I have that has this problem.

Hello auto, and welcome to Sevenforums!

I may not know a whole lot on exactly what is causing you the problems, but we can troubleshoot a bit to see if we can't find what's going on inside. If youtube works on everything else, then it isn't an ISP problem.

First, are you using the latest version of internet explorer (9)? Do you have the same trouble with another web browser such as firefox or chrome?

Second, Do you have every single "important" update installed, and all internet explorer or web browser - related "optional" updates installed? And have you updated all add-ons for all web browsers that you use, especially flash player and java?
Just what are all the add-ons that you have installed, especially any security add-ons. Please list them for me. Do you have any tracking protection lists that you might have enabled? Disable all of those tracking protection lists and check to see if it all works now (may need to restart IE).

Now we go a little deeper so gird up your skirt and let's trudge:
What antivirus/antimalware software(s) are you running? Some antivirus/malware programs can hinder normal operation, so you might consider disabling all security features temporarily and navigating to a SAFE website, such as youtube, that you've been having trouble with. If you are able to use it well, then the problem lies with your security software(s).
Note: If you've installed another firewall other than the pre-installed windows firewall, disable it now. I would go as far as removing it, but it is up to you. Windows firewall works perfectly fine (often better), and you shouldn't have to disable it at all during our tests.
Also note: Re-enable everything if the problem persists. Update your antivirus software and do a full scan on your system to make sure it is malware free. If you do not have an antivirus software, use mine: http://www.microsoft.com/security/pc-security/mse.aspx

If not, we continue on:
Try resetting IE9*: Reset Internet Explorer settings in Internet Explorer 9
*BUT FIRST: save all of your favorites (if you have them): Import or export favorites in Internet Explorer

Let me know how all of this turns out!

Yes, I am using IE9 and latest updates of Flash, Java, etc. No matter what browser I use I get a "cannot display the webpage" screen.

I'm using Malwarebytes anti-malware and I have run a full scan recently with no malicious software detected.

I have no firewalls enabled, even the default windows firewall is disabled.

That is quite a list I provided, including links and all. Surely you haven't gone through all of it just yet, or have you?

Even with malwarebytes, I would recommend a lightweight antivirus solution. The free malwarebytes doesn't have real-time protection as an antivirus does, and the paid for version isn't as good. Don't get me wrong, Malwarebytes is perfect in addition to an antivirus product. It picks up any slack left behind. Again, MSE is a good option but there are many different kinds of antiviruses. Choice is yours. Whatever your choice, please run this safety tool to check for malware (as an added precaution): Microsoft Safety Scanner - Antivirus | Remove Spyware, Malware, Viruses Free
Make sure you never have two ANTIVIRUS softwares installed at the same time, as conflicts may arise. Note that Malwarebytes is not an antivirus product, so it is completely exempt in this regard.

AFTER you finished everything else in the list I provided earlier, we shall continue:
Are you running off a home location with standard modem>router setup? Are you running wireless or wired? Does it make a difference if you switch between the two?

Failing everything (and with your confirmation that you did, in fact, do everything), the only other options are to do a repair install (I can help you on that front) or a clean install. I would think a clean install would be quite extreme at this point so hold off on that till the very last.

Oh, and there is also restore points if you know of a time when your computer was acting fine and you want to take it back there: System Restore
Read the tutorial carefully just what you will lose if you choose to restore.

If every single thing to this point fails, then post a screenshot of both your installed programs and web browser add-ons (internet explorer).

Please try to flush the DNS by using the following command and try again.

IPCONFIG /FLUSHDNS

Also empty your local cache, history etc.

Of course I forgot to include the famous Dinesh's internet troubleshooting guide. Anandntvm just reminded me:
Internet Troubleshooting Guide

Try out all the steps in that tutorial that you haven't tried yet.

Ok, I just realized that I forgot to include the fact that I have AVG Internet Security installed as well, so I DO have an anti-virus software.

Oh, thats fine. AVG is getting better as an antivirus than it used to be, but do follow through all of the steps I've listed in all previous posts, including temporarily disabling AVG to see if it is the cause of any of the problems.

Disable AVG and Windows Firewall.

Does this solve the problem?

No, Unfortunately not.

Also, I have run a full scan for malware, nothing detected.
AVG and Firewalls aren't the problem, browsers aren't, I have flushed the DNS.

Is there anything I can do to fix this problem without resetting my PC in some way?