PC randomly shutting off - wont turn on without unplugging

Hello, My PC has started randomly shutting off after being on for a while, usually takes around 15 minutes but its inconsistent.

this has only started happening in the last two days ive not had any issues with my PC before.

some details:
Its a Prebuilt i bought a few months ago- no prior problems

i have cleaned it out since its started the problem but it has continued

its not due to a loose power cable as ive knocked it about to see if that was the issue

Any and all help is greatly appreciated as I dont know very much and I just want to do work and play games🙂