Try download onyx and run automation scripts to optimize and clean everything up. If that does not work you could try zapping your pram:
As you hear the startup 'bong', hold down these four keys: Command-Option-P-R. It will bong again. And again. Continue to hold down these four keys until it has 'bonged' a total of three times (the initial startup bong and two more after you hold down those four keys).
Now your PRAM is cleaned out and uncorrupted, and the PRAM values are restored to their factory defaults.