Greetings people of Bleeping Computer!
After 2 weeks of troubleshooting, i found out that the cause of my troubles is most likely a short caused by overtightened cpu heatsink.
It all started when i changed the thermal paste and mounted the cooler back on (silentiumpc fera 3) the system would then start for about 2 seconds, shut off, start again, shut off.
I then opened the case, checked all connections and hardware positioning which seemed fine, but i re-seated everything anyway (except the cooler) the system then booted up only to show the same behavior two days later. I have tried to swap the power supply with a unit that im 100% certain works and can handle this machine without any issues - nothing changed. After this process ive decided its probably time to RMA the system and i didnt want to send it with the new cooler on as it wasnt present when i bought it. I installed the first power supply back in, took the heatsink off and installed intel stock cooler. I then tried my luck once more and the machine booted up just fine! i left it running for about 2 days, did some stress testing with prime95, heaven benchmark and some gaming - no issues. This was the time to try and install my aftermarket heatsink once more only to see the "bootloop" again. I then re-seated the cooler and made sure to only finger-tighten the screws on it and the machine works again.
i should note : all hardware on the mobo is definitely fine as it has passed hours of stress tests and memtests, i was grounded when working inside of the case, there was no thermal paste spilling where it shouldnt, checked all the mobo capacitors & none of them showed signs of damage.
now the question is - how badly could the board be damaged from this (i think) short caused by the cooler? is it still reliable ? the backplate of the cooler is plastic, but if overtightened could it press the mobo metal cpu backplate so hard to cause a shortage?
Thanks in advance for any info and please, excuse my english as it is not my native language. Have a nice day, Jan.
Motherboard - MSI H97 gaming 3
Cpu - Intel Core i5 4460
Memory - Corsair Vengeance Pro 2x8gb ddr3 @1600mhz cl9
Gpu - MSI GTX 960 Gaming 4gb
HDD - Western Digital Blue 1tb EZEX
PSU - Bequiet pure power l8 600w