The red X can be the result of many things... Blockage by your internet provider... blockage by your settings in Internet Explorer, Firefox, Safari, or Opera... Blockage by Comodo, ZoneAlarm, Kerio, or SunBelt software, blockage by one of 87 security or registry editing programs, or an inadequate video graphics card or driver.
Start with changing your browser settings, and go back to the Windows Fireall... Some days, fixing such a problem is easy, but it is usually one step at a time.