Computers can not be opened from time to time, really depressed.

Last computer on the card in the computer display screen system (XP screen) has been unable to open such a machine.Tried so many times, but then I opened the box, just knock on a few, can not think of Opened.Just another way, I have blown a few, just a few out, can be opened.Who tell me what the problem.Is there an instability.