Hi. I upgraded my mac to 10.9. Till I upgraded my mac to 10.9 from 10.8 it worked smoothly. After upgrading it to 10.9 it started lagging slightly, but was manageable. Recently after updating a security update, there has been severe lagging( taking almost 1/2 of an hour to boot and 10-15 min to open a finder window etc). Now except app store no other application opens, and finder crashes upon opening 2 or more windows or app store. Is there anything that can be done to make it normal. Please I need help. Thanks. My mac: 2007 imac, 2.0 ghz 2 gb ram.