Intel Motherboards : PC wont boot 9/10 times

hey guys,

(TLDR see below)

i have had big troubles with my PC for a while now and was unable to find a solution, neither through google nor though some hardware forums where i created threads. i hope that u guys here will be able to help!

a while ago my PC started failing to boot. all fans would be moving, but my monitor would say "no signal", the small red LED on my front pannel that indicates my harddrive is working would NOT light up, but there would be no POST beeps at all. all this started out of the blue, no hardware changes shortly before.

i tried to check if all hardware was correctly connected. i tried my 2 ram sticks separately and while trying around the PC would eventually boot and run w/o problems for hours. after shutting it down that day and trying to boot on the next day, it would all fail again. fans moving, no signal on monitor and red Harddrive led not lighting up. shutting it on and off or pressing / holding the reset button would eventually make the red led light up and the PC would boot normally and run w/o problems for hours.

i tried to find solutions/help in forums but was unable to. i then decided i would install windows 10, to see if that helped. installing worked, every time it tried to restart during installing win10 i obv had to try a couple more times to get it to boot. but it installed and for a few days nothing had changed. i was now using win10 but still had to give it a couple of tries to get the boot working.

then today after a couple of tries, windows 10 would show a BSOD during startup reporting "Inaccessible Boot Device" and that it needed to restart. after restarting (again, had to try a couple times), windows again showed a BSOD, this time giving optons to restore to a earlier restore point (didnt help), restarting and other stuff, none of which helped. restarting would just result in the same BSOD cycle again.

my motherboard is a asrock h77 pro4-m

i tried resetting bios to default which worked but did not help. i tried to open the pc and see if i could find any loose hardware and so on.

tldr:

-when trying to boot i get no signal on my monitor and the red harddrive LED is not lighting up. fans are running and no POST beeps most of the time.

-sometimes when trying again or hitting the reset button the red led would light up and shortly after my monitor would get a signal and windows would boot.

-tried my ram sticks: both sticks (dual channel, inserted into the correct slots results in post beeps and no boot, ever.) each ram stick individually results in sometimes being able to boot and if it doesnt there are no post beeps. inserting no ram always gives post beeps.

-new problem: since today even if the boot eventually works, now windows is stuck in a BSOD cyclew that tells me "Inaccessible Boot Device" and that it needed to restart after eventually managing to restart it shows another BSOD saying windows failed to boot system restore point and stuff but nothing helps.

would REALLY appreciate any kind of help. pretty sure some part(s) of my hardware are failing but how do i figure out which? isnt it strange that after failing to boot for a few times, the pc would then finally boot and run for hours w/o any problems? and next boot the same problem would start again? and now this BSOD bullsh*t...

thanks guys