You most defenitely will need an antivirus and firewall as your first line of defence.
There are very good free ones out there, but first we have to make sure your system is clean of any of these applications before you download and install the new software.
Can you download ccleaner here:
http://www.snapfiles.com/reviews/CC...
Once downloaded install it. Open ccleaner (an icon should now be on the desktop), click on the "tools" button on the left. You should have an uninstall screen open with a "save text to file" button on the bottom right. Click on this and save the file to a place easy for you find e.g. desktop.
Open the file you just saved, copy all the text and paste into this forum.
I will have a look at it later today and then we can go ahead with setting up your computer with free anti-virus and firewall software.