I own a very old - but up until about last year - once usable iMac. It's the 2007 iMac 2.0 GHz Intel "Core 2 Duo". My HDD died about 3-4 years ago and I replaced it with a 500gb hard drive. After being harassed by the automatic pop-ups from the Mac app store to upgrade the OS to Yosemite, I said hey , why not. Big mistake. My computer has become painfully slow and practically unusable. It takes about 3-4 minutes to open a safari page if its going to open at all. I mainly use this computer for school work when i'm home and want to get some usability from it again. Any recommendations? I don't know if replacing my HDD with an SSD - even if possible - will speed up my computer. Or , of course , downgrading back my OS to snow leopard but in doing so , i'd lose my data. Any recommendations? Thanks , SA.