My comptuers been a little dodgy HELP PLEASE :(?

-Basically, my computer, firstly looses signal to the moniter and then the computer bases lights turn off as though it has been turned off but it still sounds like its on, its starting to annoy me as i dont know when this little attack will pursue and i have work to do on my PC, very irratating please help, checked the power sockets and everything is in order :(