So if the new RAM doesn't make a change I'll uninstall McAfee and see what happens.
I seem to remember something going on with Windows Defender earlier on... maybe you should try uninstalling McAfee now. You can always re-install it later.
In the meantime
Here are three good antivirus free for personal use:
- Microsoft Security Essentials
- AVIRA Note: AVIRA free comes with adware that promotes their paid for version each time it updates. A small price to pay for an excellant anti-virus program
Microsoft Security Essentials together with Windows Firewall (which comes with Windows) is probably a good choice for the run of the mill user. This because it is light on resources, it is unobtrusive (it works away in the background without interrupting) and you don't have to be an expert. Firewalls have a habit of flagging suspicious files and asking the user to decide whether to accept the file or not. Often the run of the mill user has no idea about what a particular file does and just says no to everything... down the track they wonder why programs they use regularly suddenly stop working or maybe they try and download something they frequently downloaded in the past but now find they can't.
Note: Do not use more than one anti-virus or firewall. Running two or more real-time anti-virus, anti-spyware and firewall monitors at the same time can cause a conflict. That conflict can result in slow computer performance, error messages, crashes of the programs or other types of failure. You will very likely end up with little or no protection.