Ones it power off then immediately monitor did not switch on. After half an hour only get on. What will be problem and picture also not bright. (poor contrast)

change your tcon board and you will be fine

More likely to have dying power supply due to bad DC filter caps as you can see in my albums here:
Failed TV and Monitors pictures: http://s807.photobucket.com/albums/yy352/budm/

Failed LG: http://s807.photobucket.com/albums/yy352/budm/LG/

Basic LCD monitor and TV troubleshooting guide:
http://www.fixya.com/support/r6150077-basic_lcd_monitors_troubleshooting
http://www.fixya.com/support/r5093881-lcd_flat_panel_tv_troubleshooting_guide
http://www.fixya.com/support/r7406380-tv_training_manuals

Learn about bad caps: http://en.wikipedia.org/wiki/Capacitor_plague

Capacitors kit: http://lcdalternatives.auctivacommerce.com/ he can make you a set of caps for you.
Or www.digikey.com just make sure to use caps with low ESR, 105c, high ripple current, long life rating such as PANASONIC FM or FC series.
Please post back what you find.

Sounds like your monitor is going bad. You might get some more use out of it if you power it off for a couple hours and try again but my guess is this is a heat-related failure that is common on ViewSonic monitors.

I’m happy to help further over the phone at https://www.6ya.com/expert/matt_7e951e081251ffbc

your tv has a vert problem

More likely to have problem in either the backlight light inverter board or bad lamps due to poor solder connections, see http://s807.photobucket.com/home/budm/allalbums
You will need test lamp to narrow down the problem.

Start cheking power for bad caps furst, see example here: http://s807.photobucket.com/albums/yy352/budm/Samsung%20203B/

You'll need to have your power board -inverter redone.
The capacitors are starting to fail and that eventually will stop it all together.
I repair many monitors through ebay with these types of problems.
If you take it apart and send me a picture, I can usually see the problem areas.
ebays
bammbammfran

It sounds like one of the capacitators inside the monitor is malfunctioning, these little things store a certain amount of necessary power and then discharge it when it is needed.  If it is malfunctioning, it could explain why it takes so long to charge, and why when you hit it, it suddenly comes on.  

The problem is with power inverter, usually the capacitors go bad and need to changed, they might be bulged and or leaking. Very cheap fix, less than a buck apiece and an hour with a solder iron. Google it to find more info.