What causesnmy LCD Acer 24" monitor to go black for a second or two

[Lee26]

Hello,

 

[jake1496]

Hello everyone! I bought a dell laptop from www.ebay.com and a Sylvania laptop from http://www.sourcinggate.com/laptop-and-netbook-c-252.html three years ago but hadn't used them since the last year. Then I found I even can't power them up a few days ago. Who can tell me the reason? Thank you!