most likely a PSU issue since removing the GPU meant the load is a lot lower so kayang kaya na ng PSU. although, problems with PSU if ongoing for quite some time will also damage other components.
also, may AVR or UPS ba? baka naman madalas talaga ang power surge sa area mo (i.e. maraming welding shops and/or other high electric consumption machines) and either wala kang AVR or kulang ang wattage ng AVR. you are using a 700W PSU so your AVR must be around 1000W (the regular ones are only 650VA which is roughly around 400W)
in my case, sa area ko mababa ang input power (according to my AVR the input was only about 200V so the AVR is giving the extra 20V to maintain voltage). ang ginawa ko to remedy the situation better was to get a UPS (2000VA) since UPS also function as AVR and pag may biglang power adjustment may backup battery. although with my old AVR pag nagkaron ng surge, most of the time kaya naman, tutunog lang ang servo motor meaning may adjustment. kaso may mga times na hindi na kaya ng AVR (system restarts) and thats when the extra battery of the UPS will come in handy