Computer extremely slow on Windows 7!!

Recently my computer has become mind blowingly slow. I have no idea why, I have run disk cleanup and defrag and everything possible.

The real kicker is that I have my computer set up to dual boot, so I can choose Windows 7 or Ubuntu when I start my computer up: Its deathly slow on Windows but very fast on Ubuntu, can someone help me find out why my computer is so slow on Windows as I use Windows much more than Ubuntu!?!?

Thanks!!