Virus Issues

Hello,
I am going to start by saying I know nothing about computers, and I stumbled on this site by accident, so please be gentle with your wording in response.
About a week ago i was using my computer and it started running quite slowly, and by the end of the hour I was getting pop-ups telling me that my computer was infected with spyware and multiple trojans. I had symantic at the time, and it was telling my that it had taken care of the issue (hacktool, I believe it was called, but I may be mistaken about that). So I tried to continue with my browsing, but it was running too slow so I re-started. When everything was done loading my background screen had changed to a big sign that said you have been infected with spyware, system has been disabled, don't use your computer blah blah blah. So I ran a scan with symantic which said I was clear. In the next week I have gone through that situation over and over and over, running scans, my computer saying it was clear, then getting messages that I am infected. I finally asked and IT person at walmart (yes, I know, but their advice is free compared to say geek squad) and they said that the virus protection had probably run out, shich is why it was saying there was nothing there. So I bought McAfee, but not I can pull up and internet browser. I can connect to local wireless networks, but if i try to browse I just get a blank page. Please someone help!