Alright, so admittedly this video will not help you fix all possible backlight issues with a Dell P2210T, but it may help you fix the most common problem I’ve seen. I have a lot of these monitors in production (many were deployed in 2012-2013) and most of them have exhibited the same issue: 4 failed (swollen) capacitors on the power supply circuit board causing the monitor backlight to turn off permanently. The fix is relatively cheap if you’ve got some soldering skills/equipment and an hour of free time.
330uf 35V capacitor (3 of them needed) – $4.25 for 6 at Amazon (https://www.amazon.com/Panasonic-FM-Radial-Electrolytic-Capacitor/)
220uf 35V capacitor (1 of them needed) – $12 for 10 at Amazon (https://www.amazon.com/PANASONIC-EEU-TP1V221L-CAPACITOR-RADIAL-pieces/)