Dear experts, I wondering whether all of you could help me out...
My CRT monitor sometimes dies off suddenly. Whenever I hit my PC case, the monitor turn on again. I am using an all-in-one motherboard. I am wondering, could it be because of my motherboard driver, or there is some defect with my monitor? Would procedure would you recommend me to troubleshoot? Thank you for helping out.

So the video is on the motherboard? You don't have a seperate video card then right? Could be a few things, bad on board card, bad motherboard, bad monitor, bad port, or bad end of cable on monitor. To trouble shoot, try that monitor on a different computer, and try a different monitor on that computer. Then we can see if its the monitor or the computer at least, then go from there.

Sounds like a bad connection, check all cards/cables are seated properly, disconnect and reconnect all ideally, as metal contacts can corrode affecting normal operations, if you only have to whack your case to solve the problem, then it isn't going to be a disastrous h/ware fault.