Problem: Monitor would turn on for a couple of seconds and then turn off. When on a faint squeal could be heard and the monitor brightness was reduced from normal operation.
Solution: Clearly a backlight power supply problem, I opened the monitor by removing the base and the 3 screws from the lower back of the monitor. The case is one of those 'prise-apart' packages with 3 snap locks on each side and a few at the top. Pushing the front section in whilst pulling the back away seemed to do the trick. I still hate these things.
Once inside I managed to get to the power supply. This involved removing the metal plate on the left (two screwdriver prises and it pops off), unplugging a few cables and sliding the metalwork to the top.
Once the PSU was unscrewed it was obvious from the bulging tops that three capacitors required replacement. These were C113, C112 and C316. Two of these are 820uF 25V, which can be replaced with 1000uF 25V (case size is 10x20, however 13x20 can be fitted with a bit of a squeeze). The other cap is a 470uF 25V which is easy to find a replacement for. Once replaced and re-assembled the monitor performed just fine again.
This has also happened to my second monitor of this type, so it is probably a comon fault. Here's a picture showing the three caps that require replacing and also of the offending bulging caps taken out.
Caps marked are the usual culprits
Capacitors show clear signs of stress
Almost exactly the same problem occurred in a Samsung 40" LCD TV. There are 4 x 1000uF 10V electrolytic caps in the PSU that blow their vents.
Replace them with 1000uF 16V caps and the TV is back to normal. Similar symptoms too, where the TV will require several attempts before it turns on. This seems to be a recurring problem, where substandard or under rated caps are used in power supplies.
Not sure if it is intentional, to render the device inoperable after about 5 years, or just cost cutting by manufacturers. Maybe a bit of both.