A quick Google throws up a bunch of useless information most of which is a disguise for selling you some 3rd party software solution. So I started with the Microsoft suggestions "Optimise Windows 7 for Better Performance".
First suggestion is to try the Performance Troubleshooter, which can automatically find and fix problems.
- Open the Performance troubleshooter by clicking the Start button , and then clicking Control Panel. In the search box, type troubleshooter, and then click Troubleshooting. Under System and Security, click Check for performance issues.
There are other things you can do, if you are not certain about the security status of your computer you may wish to double check you have no nasties lurking about on you HD. Make sure your ant-virus software is up-to-date and run a full scan. If you don't already have it, upload anti-malware software such as Malwarebytes, get the free version here. If you not up to speed with security software I suggest you have a look at this video by Britec09 on YouTube, this guy knows what he is talking about and there are no catches.