Help!!! Macbook pro running really slow.

Help! I have a 2011 Macbook Pro 15" 2.2 ghz. Suddenly it has started to run extremely slow that it is unusable. I checked activity monitor and I see loginwindow and finder using 100% cpu. But when I log into a different account the Macbook pro runs fine. I don't know what to do and I have tried repairing permissions and deleting loginwindow plists. Please help.