NSIS error when trying to install!

hello there

i am planning to switch from UDK to Unity

However, when i download the Unity Setup File and try to install it ,it says NSIS error I Reformated my entire HDD and Reinstalled all drivers with a fresh install of windows 7 64bit but the problem is still there.

I've also tried all possible and plausible solutions mentioned on forums,NSIS help..etc

Please suggest me what to do now.(and i am sure my pc is absolutely fine)

I tried on my laptop too . It didnt work.