I was on Mavericks, then computer started acting really slow a few days ago. I thought upgrading to Yosemite might help over-wright what ever the bug might be, but no. The symptoms are slow responses whether bringing up applications or even typing this message I randomly get the Beach ball as seemingly the CPU has to think about me just typing a word - no other apps running. I had been on Mavericks for a few months with no issues. This is on a late 2009 iMac 27 with 4 GB of ram, i5 2.66 Mghz processor, yosemite 10.10.2. I do have a back-up OWC HD with time machine. I could restore to one of the previous states. Should I try this first?