Well, you DID have Sirefef, you ran the removal tool and it found it. But another thing Sirefef does is it will wreck your Windows Firewall.
You have to repair your Firewall, open your Network center, and check your firewall, if it is not running, try to start it. If it will not run, try this.
Diagnose and fix Windows Firewall service problems automatically
And, I have to tell you a Sirefef infection is NOT easily cleaned, the main parts of it were taken out by the tool, but the SOURCE of it may still me in there, and it will re-infect you.
Check for something called the Tarma Installer, it will be in your User folder under Appdata/LocalLow, you have to enable viewing of hidden system files and folders to get to it.
Also, AVG is not sufficient to remove Sirefef leftovers, delete it, and download Eset NOD32.
Also, there is a HIGH probability that your Windows Defender program has been hijacked by Sirefef, You will know this if you tri to install Eset and you are blocked by Defender from installing it.
If this is happening, you have to boot to Safe Mode and RENAME the Windows Defender folder, to Windows Defender Old or something. Then you have to rename the MSASCui.exe file to MSASCui.rubbish or anything you want.
Sirefef is just about the worst virus you can ever get, if you have installed OpenCandy, Tarma, Delta toolbar, or anything similar, you have installed it yourself. I think this is your main problem, you still have components of Sirefef in your system, the removal tool is just to stop it from running, you have to remove the programs that had this dandy program attached to it.
Running toolbars is simply not a good idea anyway, I use Yamicsoft Windows 8 Manager and in the Network/Internet Explorer Section, you have to BLOCK all known toolbars. Even if you use Firefox or Chrome and not IE, you are not immune to these hideous pieces of crap.
AVG especially the free version is NOT going to help you in any way, it is simply not good enough to get rid of this, it's too powerful.