Question My PC keeps restarting. What might be the problem?

[Ebtisam]

Hello everyone. So I've been facing this problem for about 8 months now. Basically what happens is my PC restarts quite frequently whenever I do professional work like photoshop, lightroom, Autocad, etc. This problem started when at first when I installed any game. I played for quite some time. Then the next day, whenever I turn the game on it just automatically restarts. Then it started with everything, whenever I'm doing work or even using chrome, after a while, the PC just happens to restart. But I reinstalled my operating system i.e Windows. Then the problem was solved temporarily. I was working without any problem. Then again I installed the game. And the problem kept happening again and again. What might be the problem? Is it my power supply? Thank you.
My PC Config-
RAM- 8Gb ram 1500 bus
GPU- NVIDIA GEFORCE GTX 750 Ti 6Gb
Processor- Core i5 4460
Motherboard- H97 Gaming 3
PSU- 450 Watt

 

[Phillip Corcoran]

Make, model & age of PSU ?

 

[Ebtisam]

Hello! It's an Antech one with 450W. Bought it in 2015. Pretty old. Upgraded nothing since then.