My computer isn't booting correctly. Sometimes it goes into windows and everything's fine, but more often that not it doesn't do anything. The fans start, but nothing is displayed on the monitor, not even a black screen, just no signal. I don't know what to do.

Try changing the sata port or check that your boot drive is set as the highest boot priority in the bios.

take out the mainboard from the case boot it up outside the case, maybe you the motherboards makes a short cirquit some where, somethimes. cause you  use a wrong screw or tieded it to tied..