Unfortunately there can be many causes to freezing and that is why there are so many solutions that work for some and not for others.
Make sure you are not infected with malware (virus/keyloggers/etc).
Make sure you have the latest drivers.
You should be running W7 Service Pack 1 which included a hotfix for some known issues.
For custom built machines it is very often RAM incompatibility or voltage/timing settings and generally accompanied by BSODs so verify you have the right memory and settings.
Sometimes it may be as simple as setting the power options to maximum performance and disabling options like "allow the HD to sleep/hibernate".
ALL AV software will slow the machine to some extent but they vary greatly and what seems to slow one machine works pretty well on another so you may need to try different Antivirus software. And of course if you HAVE a virus that can slow things down or even stop or trash your machine so running without AV is not a valid solution.
A rotating circle means "processing" so something is running (when you say jitterring do you mean something besides rotating?).
It could be a problem with your anti-virus or it could be you are infected with a virus. It could probably be a lot of things but I would probably start with a system repair from the W7 DVD and then I would probably try a virus scan with an online scanner or maybe malwarebytes. See the Freeware DB.
I would also try updating your mouse drivers to the latest version.
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