Sometimes with anti viruses even with permissions set, sometimes if they are running a firewall it can be disruptive. Have you gone into your browser settings and changed the security options in there?
I personally run norton 360 and it's the only one I recommend. If you like free software Microsoft security essentials suffices.
I would check your browser security as a second guess. Have you installed java and done all the updates? Another thing you could try is downloading safari from apple and seeing if it runs there, those are my only suggestions from experience. I run 5 pc
's all home built and each one has different issues from time to time.