You have a really powerful processor. It is possible your RAM went bad, so follow this thread:
http://www.sevenforums.com/tutorials/715-memory-diagnostics-tool.html and check to see if your RAM is good.
Did you disable any services in services.msc on your computer, or tamper with the registry in any way?
Is your Hard Disk full? What was going on when you started noticing a difference in system speed (items that were recently installed, settings that were changed, etc)?
It could be a virus. like i said, you should try uninstalling all virus protections on your computer and install the microsoft security essentials and malewarebytes (i gave you links in previous posts) and they should be able to detect any problems after they are completely updated and have a full system scan performed (they usually try to perform a quick scan; do the full scan instead. this may take time. You can do a repair install of windows 7 through this tutorial here:
http://www.sevenforums.com/tutorials/3413-repair-install.html
It wont help you if you skip things to save time, such as the memory diagnostic or defragment or full security scan. These things do take time and you will just need to be patient in order to sort it out.
Did you install anything recently? You may look into (if you have it) going back to a previous restore point when your computer was acting normally through this tutorial:
http://www.sevenforums.com/tutorials/700-system-restore.html
Warning
A System Restore will also uninstall programs and drivers (step 8 in Option One) that were installed after the date on the selected restore point.
Failing all of this, unless someone else has a suggestion, it is either a hardware problem (could be a motherboard malfunction or any number of things, but don't start buying things unless you know for sure) or it is something that can only be solved through a complete reinstall of windows.
If everything fails, you might see if any warranties cover a failing computer or take it in to a computer repair store. I have run out of advice, unless I have a whole lot more details, such as recently installed programs or any guess as to why it should be slowing down.
Let us know how it goes, I wish you luck, and if you happen to solve your problem, it may help others if you mark this post as "solved" by clicking the red white and click triangle in the corner of your first post and typing in "solved" and sending it off to a moderator.
Happy American Independence Day to you and your family