Grif has good advice here re: getting Malwarebytes to install on your computer: http://forums.cnet.com/5208-6122_102-0.html?threadID=352109&tag=forums06;forum-threads
At this point are you sure that you only have one anti-virus installed and running on your machine?
I have recently had a problem with my anti-virus software preventing me from accessing my Sky broadband. The internet will only work if I uninstall all anti-virus protection.
I originally had AVG and this was working fine and then this problem occured. I took advice to change software and moved over to McAfee but the same problem has occured. Since then I have tried downloading free anti-virus software but none of them can setup correctly.
I was advised that malware may have infected my computer so have downloaded malwarebytes, but this has not helped, particularly because I can't update it (malwarebytes.org comes up unavailable when I attempt to access it.)
Could anybody please give me any further advice on what to do? Thank you.