Never Guess!
An incorrectly installed cap will either blow up (blow it's cap so to speak

) or ruin some other part of the monitor or simply not let the monitor work right/at all.
There should be indication on the circuit board that will fill in an edge of the circle on the top of the board. This helps you identify the polarity.
Some caps are bipolar and don't matter, but are marked as such. Most however are polar and must be installed correctly.
Find the manual and triple check them.