This can be caused by many things. The first thing I would look at is your hard drive. How full is it? How many programs are running in the background? Has it been defragmented and optimized lately? Does it have enough RAM for running your current system and programs, again, what's running in the background?
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To find out what’s running in the background do a “Force Quit”, by hitting Command + Option + Escape.
This can be caused by many things. The first thing I would look at is your hard drive. How full is it? How many programs are running in the background? Has it been defragmented and optimized lately? Does it have enough RAM for running your current system and programs, again, what's running in the background?