A failing power supply will cause all kinds of issues, however, I do not have my hands on your computer to diagnose and cannot say with certainty it is your power supply.
It sounds like you have a hardware problem. If you do not have them download CPUID HWMonitor [free version] or HWiNFO [32 bit or 64 bit depending upon what operating system you have, if you do not know, if you are using MS Windows, right click on computer or if Windows 10 open System [found by right clicking the start button or in Control Panel > System and Security > System].
https://www.hwinfo.com/download.php If you have a 32 bit operating system use 32/64, if you have a 64 bit OS, such as Windows 10 64, for example, use the HWiNFO64 download installer, it is free.
Make sure nothing in your computer is running over 80 degrees C.
A CPU under 100% load at 50 degrees is good. To stress individual components, download SiSoftware Sandra [free]. For example, to just stress the CPU, run just the Processor Arithmetic and check for temperature spikes using HWiNFO or CPUID HWMonitor [free version].
Sometimes a weak component can be spotted by simply increasing voltage, for example, go into the motherboard BIOS and turn increase RAM voltage by .025 then see if you have the same problem, if you do, decrease the RAM voltage to normal and increase the CPU voltage by .020 volts. If that does not work decrease the CPU voltage to normal, turn off your power supply unplug it if there is no switch, open your computer case and remove all RAM, except one stick. Boot up and run a test to check for stability. If you still have a problem, use the same single stick of memory and place it in each RAM socket, reboot after placing it in a new socket and run a test. If your computer still fails testing, try every stick of RAM, one stick at a time, in every socket. You want to find a possible bad stick of RAM or RAM slot.
After a period of time any component that is socketed or connected in any manner can fail to provide signal or voltage due to oxidation or differing metals. So, sometimes simply turning the power supply off, disconnect then connecting every socketed item 3 times, and disconnect and reconnect everything else 3 times - including cables from USB to video cable to USB cables to modem - everything. Before disconnecting power cables from the power supply to the motherboard or anything plugged directly to the power supply, unplug the power supply from the wall first.
If after all of that you still have a problem you will most likely need a GOOD repair facility to find the problem for you. Hardware problems are often difficult to detect.
If temperatures are good you have a hardware problem somewhere and it may be difficult to find.
By the way, after 3 years many thermal interface materials fail [get brittle, separate, turn to powder and so on]. You should use a good TIM, such as GELID GC-EXTREME on your CPU and any chips on the motherboard that have a heatsink on them - all except those that use pads - the TIM should be replaced. If you do not know how to do this you can check youtube for a video, just remember some of those people do not have over 30 years experience with computers as I do, therefore some do not provide the best or even bad information.
To replace TIM on a CPU do not use a metal based TIM, even Artic Silver 5 [its components separate over time, leaving hot spots], get a paper towel or a clean dry wash cloth, some coffee filters and 91%+ alcohol, turn the power supply off, remove the CPU heatsink and using a paper towel clean most of the TIM from the heatsink and the CPU, being careful not to tear or rip the paper towel, if something tares the paper towel use a clean dry wash cloth, finish the job with the alcohol and coffee filters, they do not leave particles behind such as a paper towel or wash cloth would. Apply thin lines in the form of an X on the CPU lid. You can check to see of the CPU is completely covered by removing the heatsink after it has been installed. [NOTE: I remove the CPU from the motherboard and place it on a non-conductive surface, if you spill alcohol on the motherboard you will need to wait until it evaporates before turning the computer on.]
Please post your findings here. Thank you.
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