I have a problem on one of my computers. I am running Ubuntu 11.04 and
it is freezing up. When I check system monitor, the cpu usage is at 100%
and stays there. Checking the processes tab shows that the only thing
using the cpu is the system monitor and it is only using around 10%.
I even created a new account and without even doing anything, it is the
same.

Have you checked the CPU fan?

The fan is working OK. The computer is only about 3 months old.

I would try a different desktop environment still on 11.04 to see if Unity/
Compiz is to blame. You could install classic GNOME, XFCE or even Unity 2D
to see if it runs better. If it does then you can blame Unity. If it doesn't
then it is likely something else in 11.04 itself or the graphics card
driver. Unity with Compiz is slower than GNOME classic and may not work as
well with some graphics cards. The biggest changes in 11.04 are related to
the switch from Metacity to Compiz and GNOME classic to Unity. To switch
desktop environments you logout and change the session and log back in. You
likely know this but others may not.

You might take a look at the log files in /var/log (most easily viewed with the
log file viewer under "System" | "Administration". Start with the system log,
and look for a flood of one kind of message.

(I identified a bad or incompatible Ethernet card that way, once.)

Are you viewing all processes, including the system ones, or just those
you've started? If you go to the View menu in System Monitor, there's
an option in there to see all processes (for some reason, I cannot get
my own system monitor to start, so I can't give you the exact details,
sorry).