when your OS is running press Ctrl+ Shift + Esc, got the the processes tab, and click on the CPU tab on the list there and see what programs eating up your CPU, find out what it is and see if it's safe to right click on it and end the process, also you may have recently installed some maleware, I would boot up in Safe mode - http://dottech.org/25365/tip-tapping-f8-not-getting-you-into-safe-mode-try-holding-f8/
and run a maleware removal tool, or just try using a Windows restore point, also turn off all un needed start up applications that may be hurting performance, http://www.groovypost.com/howto/performance-disable-startup-programs-windows-7-vista/ , and after all that if you boot back into your OS and it's still sluggish it may be a hardware issue.
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