Welcome to the forums,
Could be lots of things so more information would help. First, E:\ drive? You aren't running a live cd are you, or worse a live wubi?That's not the most responsive way to run a system.
Second it would be a good idea to take a look at what's running. I like htop and it's easy to get without using compiz. First open a terminal with Ctrl+Alt+T
sudo apt-get install htop
to get a list of processes in order of cpu use. That will give you an idea of where to go next.