Question No display or led light

Sep 24, 2020
After removing cpu fan and putting it back no signal on display on monitor, after again removing and changing fan position as I thought maybe I put it wrong side there, was still no display + the led light wasn't turning on after changing sides. Had the same problem months ago, because I did everything the same, just forgot to never do it again.

After the first time I went to a repair man, he fixed it I even asked about thermal paste he said he didin't even touch it or there is no need in reapplying it. This time I removed thermal paste and reapplied it cause I thought maybe thats what it needs, I was blowing dust off it and had an idea maybe I had [CENSORED] it up. Removed everything and unplugged from case, left psu and power cable. Not starting(if it even should, I have no clue about pc engineering). Any clues what else might be wrong because I'm totally green on this and would like to save a trip to the repair man?