Question Computer sometimes doesn't display image

[Dmconstant]

My friend has a pc which sometimes when powered on simply doesn't display any image, not even the BIOS screen, although it sends energy for the peripherals like the mouse and keyboard (but they are unresponsive, so for example when you press the caps lock the indicator light doesn't turn on or the mouse rgb doesn't change like it should). when rebooted it continues without image but then after a while (days even) it boots up fine. when we opened it, the components seems alright, without noticeable faults.

the full specs are: MSI H310m PRO-VDH
i3 9100F
12gb ram corsair
rx 550 4gb
ssd 120gb
hd 250gb

 

[rgd1101]

12gb ram? mixing ram?

make and model of the psu?

 

[Dmconstant]

it used to be one 4gb ram stick and another 8gb, both by corsair and all, but it this issue has appeared back when my friend was only using the 8gb stick. The psu is a 500w atx made by TDA, not 80 plus certified.