Windows 7: Can't access certain webpages; exempt pages from being blocked?

Hi,
I've had trouble opening certain webpages for a while and was wondering if there is a way to manually exempt certain addresses from being blocked? I have the same problem with different browsers.
This problem started when I installed a few programmes (spybot, zone alarm, and malwarebytes) a while back to take care of another problem. Since then, I've had trouble accessing random sites, most of which I can, however, access fully again, or they'll at least load after reloading several times.

Some pages I just can't access, though ("Connection closed by remote server"). I'd be grateful for any suggestions where this problem is coming from, and what I can do against it? Also for an idiot-proof answer cause I'm quite terrible at this stuff



Thanks!!