Are you talking about your PC's general performance or about your PC's network performance?
If you're talking about network connection performance, maybe your connection speed is not enough to satisfy your needs or there are too many programs and/or services running that consume a large amount of the available bandwith, thus resulting in poor network
performance.
If you're talking about your PC's general performance, you could perform a full antivirus/anispyware scan of your system to verify that it is malware-free; then you could get the complete list of the programs and services loaded and executed at the system
startup and decide to turn of or completely remove some of them.
Bye.Luigi Bruno - Microsoft Community Contributor 2011 Award
There is an amazing pack of free network admin tools.
click here to download it