Question Computer doesn't turn but motherboard light turns on

[Bless0911]

I recently bought a desktop and immediately upgraded it. I installed ram sticks and a graphics card. The PC seemed to be running perfectly for sometime up until one day when I just switched it off and it was completely unresponsive the next day. It didn't show any signs and I was constantly checking the temps to make sure it didn't overheat. Afterwards I tested the CPU, GPU, PSU, RAM and even the HDD and they were all working. Now I don't understand what the problem might be coz the motherboard light switches on which means it is getting power but when I push the power button there's no response. What might be the problem?

Edit:

CPU: E7500
Motherboard: Not sure but it's not a fancy motherboard
Ram: 8gb ddr3 1333mhz
HDD: WD 1TB
GPU: GT 730 2gb ddr3 128bit
PSU: Corsair VS450 450w
OS: Win 10 Home

Forgot to say I didn't use it for demanding tasks it was mostly used for storing data, watching videos and low-demanding games

 

[Lutfij]

When posting a thread of troubleshooting nature, it's customary to include your full system's specs. Please list the specs to your build like so:
CPU:
CPU cooler:
Motherboard:
Ram:
SSD/HDD:
GPU:
PSU:
Chassis:
OS:
Monitor:
include the age of the PSU apart from it's make and model. BIOS version for your motherboard at this moment of time.

I recently bought a desktop and immediately upgraded it.
Since you mentioned upgrading it, we'll be seeing two sets of specs, one for before the upgrade and one for after.