$12 iMac WITH ISSUE - Help!!

The iMac keeps restarting, sometimes it doesn't even get to the login screen. Does anyone have any idea on what the issue could be? I’d love to know if someone knows a solution as this would be a great everyday driver if I upgrade to a cheap SSD iMac 2010 3.2GHz, 12GB RAM, 500GB HDD, 21.5" display, fresh install of High Sierra. Will I be able to run newer versions of MacOS with open core legacy patcher? What’s the realistic newest OS that would work ‘well’ for stuff like internet It can of course be used as an external display for another Mac - I reckon it’s worth the price even just as an external display (using the thunderbolt/mini display port connector) What do we think, fellow Mac nerds?