desktop issue

so i was on my computer browsing the web i went downstairs came back and the computer was off. i tried to turn it back on and i am not getting any power.
i have tried checking all of the connections power cable wall socket etc, i opened the case checked all the connections inside all were correctly seated. i have also reseated everything inside and used the power cable from my other pc also ( it is powering the computer im using now )
there was no short circuit in my house as my electrics did not go off, there are no beeps when trying to power the pc also pc is clean inside
im thinking my power unit might be dead
what do you guys think any suggestions
 
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