Ihave an airsoft pistol and i needed to take it apart to repair it and i lost some screws that were tiny and i dont know what they are called and i was wondering if anyone knows what they are called

Ihave a singular monitor that is a tv for my computer. recently, i took apart my computer and put it back together. when i put in the hdmi cord and booted the computer to see if it worked, the computer turned on fine but the screen was blue with "hdmi no signal." i've tried everything that doesn't require buying spare parts, any answer is appreciated!