Which should ALWAYS be considered when making rational decisions ? A) the real dollar amounts of the items B) whether to use fiscal or monetary policy how many opportunity costs there are D ) marginal benefits and marginal costs?

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!