Boot to safe mode.
Does your anti-malware, whatever it is you did not say, now run?
I have a Dell Optiplex 755 running Windows 7. After being away for the weekend, I set down at my desktop and find that it is slow to respond if at all. It is connected to the internet, but I cannot get any of my browsers to open unless I reboot. I have IE, Mozilla, and Chrome. If I do happen to get online, it will operate for 10 minutes or so and then when I click on a link or another page, it will not respond and "(not responding)" appears at the top next to the URL. I can try to close the webpage and it will not respond or is very slow. I uninstalled the Mozilla as something like this has happened before with Mozilla, just not as bad. But it also is happening with IE and Chrome. I have McAfee Total Protection and it shows no viruses. I have tried top run my Anti-MalWare but it will not open and whenever I reboot, an icon pops up stating the Malware is not updating. I try to turn automatic updates on, but no go. Help!