windows 7 - Cannot access some websites

I am experiencing a rather odd problem. I cannot go to some internet sites like ucla.edu, microsoft.com or samsung.com

What happens is that the sites start loading elements (sometimes they don't) and then just keep loading forever. When I ping these sites, either I get "timed out" or "general failure". I managed to narrow down the problem to the Windows installation as rest of the computers in this network can go to those sites with no problems. Additionally, I hooked up my phone's internet to this computer and it acts the exact same way. The rest of the internet and the computer in general work fine.

What I've tried:

• All kinds of antimalware scans - they didn't find anything except for a few tracking cookies
• Various browsers (I am usually on Opera)
• Changing DNS as well as flushing the cached DNS data and other temp files on both Windows and browser - when pinging the addresses do return the correct IP anyways
• Checked out the hosts file - it's clean
• Fiddling with the MTU - tried lower values to no effect (other computers in the network use 1500 with no problems)
• connecting to the sites though a proxy, they work through a proxy. So, I am assuming that this Windows installation can't connect to the IP addresses rather than the web addresses
• I have no software firewall; the hardware firewall also applies for other computers in the network which have no problems
• tried fiddling with internet security/privacy options (even though I don't use IE), no effect

The Windows in question is Win7 SP1 with all the latest updates. The problem started out around a month ago but i haven't had the time to deal with this until now, the windows installation is around 1 year old. I really do not want to resort to a reinstall since last time it took me a whole day to get all my programs installed and the rest of the week to remember all the custom settings everywhere...

I can see some nifty malware that somehow slipped through targeting microsoft or samsung but ucla? Other than a freak corruption of a windows setting somewhere, this makes no sense

1. Run Malware Bytes or SpyBot S&D to make sure there isn't anything else (malware/spyware/adware) messing with your system.

2. Update definitions and run a complete virus scan. An additional free online scan at eSet just to make sure its all gone might be a good idea.

3. Once you know the system is clean, open an elevated command prompt and run SFC /SCANNOW to run the System File Check. When it is done, reboot.

4. Flush your DNS as suggested in this answer; Some sites work, some don't

Please try hotspotshield if the sites are loading well , then you dont have problem with whole windows settings which means you have problem with Internet Service Provider might be temporary network issue.