The sound that a PC makes at startup is part of the diagnostics process.
PC motherboards usually provide audible error codes in the form of long and short beeps. A search term like motherboard brand or PC model (if you've got a premade PC) and beep codes will usually give you the translation.
If your boot drive is a HDD as opposed to an SSD, whether you can hear the hard drive making the usual clicking noises on startup is important. If it makes click noises that are not usual (e.g. long repetitive
If you've got an Intel PC with a discrete video card then pull it out and plug the monitor into the video port that's built into the motherboard.
Then again, I assume you've been through this sort of thing on the other forums you've mentioned... if poking around the internals of a PC is not your thing, just dump it onto a computer store to fix
Yeah, I reseated pretty much everything I could before making this topic. Seems to be common but good advice though.