I am working on a Windows 7 (Home Premium) machine, SP1 on a Dell laptop.
Quite recently I started getting "Cannot connect to server error" for only some websites (Gmail, reddit, etc) out of the blue, while I was able to browse other websites easily. The first solution that worked for me was " ipconfig /flushdns" (i.e. flushing DNS). Moment i flushed the DNS the websites were easily accessible.
But now it appears I have to flush DNS more than once everday as I am getting "Cannot connect to server error" on websites. I suspect by flushing DNS i am solving the "symptom" and not the actual ailment. If anyone can throw some light on this, it will be really helpful.
Well the only solution that appears to be working as of now is "clean-installing the OS"!