What are the reasons cannot reach s few sites?

[Vrindavan]

What are the likely reasons cannot reach s few websites?

The current conditions
- those sites are working, no ip blocking
- people using the same isp can go to those sites
- have been visiting those websites all the times in the past
- i cannot go to those sites using direct ISP connection
- i can go there using proxy server or hide my ip address
- no know spyware found yet