Question PC sometimes doesn't come back from sleep / start from the first attempt

Jul 18, 2020
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Hi,

I left my PC completely unplugged from the outlet for a few months and when I switched it on, the monitor wouldn't displayed no signal. The fans, however, were spinning and lights working. It took me 4-5 restarts to turn on the monitor and I was forced to go into the BIOS settings again (they were reset). After that, I've never unplugged the PC.
Now it's working normally for the most part, however sometimes (maybe 1-2 times a week) it just won't come back from sleep or won't start from the first try.

My specs:

i7-8700k
Asus z370
RTX2080Ti
16 GB DDR4 Corsair
HDD Seagate 2TB and 512MB SSD Samsung Evo
PSU 850W Corsair

I've browsed the forums and the general consensus seems to be either the PSU or the mobo are to blame. I'm not sure how to troubleshoot it though and if I should be concerned at all.

Thoughts?