I had that problem n nothing worked, takin out lithium battery, disconnecting dvd drives, running one stick or no memory for getting the beep alert, reseating the video card... the problem is either troubled psu, dead cpu or mobo. Test separately each component, taking them to a local store for testin em out if theres no other way for u to do it.
Anyways keep hav a look at new suggestions, not every system responds the same