Slow Computer

Hi! My computer is running slow lately. I tried to defrag yesterday and it became faster, but now it's quite slow again. My physical memory is almost always at 90% because of Chrome, and it takes a few seconds to switch tabs or switch programs. Before, I can use Photoshop, Chrome, iTunes, and other programs without problems. Here are the specs of my computer: Windows 7 Professional 6.1.7601...