Computer shuts off randomly, mostly during first few seconds of bootup

So I ran memtest;

both cards on the 1st and 2nd slot: passed 8 passes

both 1st and 2nd card on the 1st slot: cpu powers on but no display on monitor. (fans power button working)

weird, they dont work on the 1st slot and yet it recorded 4gb when i insert both cards in the 1st and 2nd slot

Both 1st and 2nd card on the 2nd slot: passed 8 passes

Both 1st and 2nd card on the 3rd slot: same thing, cpu powers on but no display.

Both 1st and 2nd card on the 4th slot: passes 5 passes.

However, if i place the 1st and 2nd card on the 2nd and 4th slot, the computer goes into an infinite loop with no display.

You may have an error with your CPU, the memory controller is built into this. Can you confirm if it is channel A or B that is not working. I had a similar problem and it turned out to be a bent pin on the cpu socket that was causing the error. It was fixable. This is only for diagnostics to try and find the problem.

Or as you have found a stable configuration, you could stick to that and see how it goes.

Using my previous configuration of both my ram cards on the 2nd and 4th slot, the same problem persists after a few days of it working with no errors. how do i check the channels A or B?

Look into you bios to see what channels you are using, this is only possible with some bios`s.

I didn't have a chance to check the channels on my bios, problem still persists. I managed to boot up with this error message hard disk s.m.a.r.t command failed

Check the channels as suggested. Then test the RAM again overnight to stress test it in each working configuration.

Test the HD using maker's HD Diagnostic extended CD scan followed by full Disk Check

Try swapping the RAM sticks.