Yesterday, my Mac started running very slowly. The OS as a whole is very slow, rather than just one specific program. It has never behaved like this before, and I cannot recall any specific changes that would make it behave this way. My Time Machine back-up has also been "Preparing Backup..." for a few hours now. Not sure if this is related, but usually it does not take this long to prepare. I have tried SMC reset and repairing my disk in recovery mode, but these have not helped. Any further suggestions would be greatly appreciated. Very many thanks, Aaron MacBook Pro, OS X Mavericks (10.9.2), 2.9 GHz i7, 8 GB memory.