what voltage can be dangerous in an lcd monitor to change it?

The rating in Micro Farads (uF) is the key thing - always try to match exactly if you can.

The Voltage rating shows the tolerance of the capacitor to the voltage across it - if you put in a 10V capacitor when the old rating was 25V the capacitor will fail - a 25V capacitor may be replaced with a 35V one no problem - as long as the Voltage rating is same or higher then it will be fine.

In some equipment (not your laptop) capacitors (large ones) can hold a charge and give you a shock even when the power is off.

Peccavi
March 2010