Certain website can't open

Hi everyone,

I was thinking to download ubuntu 14.04, so I went to the official website on my MacBook pro, but all three browser on my mac can't open it(safari, chrome, opera), I'm using hotspot internet from my smartphone, most websites pass except this, I even check the firewall and it is off, anyone facing same problem? Please help me!!!

Note:

My os x 10.9.3 is installed using USB flash drive

I facing this problem long tune ago but never take it seriously until now