If you're running into system performance problems, a useful tool on Windows 7 is the Performance Monitor utility (Perfmon). The fastest way to run this utility is by running 'perfmon.exe' from the command prompt or from the 'Start >Run' area.
In Perfmon, you can run a pre-defined 'System Performance' report available under the 'Data Collector Sets > System' area; just right click on 'System Performance' and click 'Start', as shown in Figure 1. The report can take a minute or more to complete, and after that a time stamped report is available over at 'Reports > System > System Performance', as shown in Figure 2. In the report you will find a plethora of CPU/Network/Disk/Memory information, but more importantly a Performance/Resource overview section highlighting any issues that Windows might have detected that could be triggering the performance problems. In Figure 2 the system was running slow due to excessive paging resulting from available memory being too low.