I have a Mid 2007 imac with 4 gigs of ram and running yosemite. My issue is that most of the time it runs great for what it is. I mostly use it for surfing the web and listening to music. I realize it's an old machine and i'm thankful for the 10+ years it's given to me. Lately it has been freezing on me and sometime i'll go to work and come home and notice that it has restarted on its own for some reason. I am hoping to squeeze some sort of life out it as a back up computer. I was wondering what steps i should take to check what hardware may be malfunctioning.