1) Do not think you had a power surge, The system iinterpreted you flipping the Rocker switch off at the back as a surge vs a Lose of Power (black-out).
2) Yes flipping the PSU rocker switch off can create a problem, It all depends on what the computer is doing when the switch is turned off. Most cases will just give a error message asking if you want to start up in saft mode or resume Normall mode. However if the System happens to be writing to the file allocation table, or the location of writing gets hosed and it writes to the MBR, your data be be lost.
3) Need to determine cause of freezing, is it Ram or Heat, or a PSU issue.
.. Down load Prime 95 and run in blend mode (default). this will (1) test memory and CPU for errors (stability). (2) Monior temps (look at individual 4 cores) for eccesive temps. (monitor PSU Voltages, Primarily the + 12 V My Min recommend value is 11.6 V (spec is 11.4 Min). Also +12 V should not drop more than +0.3 V between Idle and load.
To test GPU (also loads the +12 V rail) run Furmark, this time monitor GPU temp and the +12 V rail.