PC turns on but doesn't boot up.

ok so this has been happening to me since 1 month but at that time it wasn't this much worst.
the problem was whenever i restarted my pc for any reason,it first turn off and then woof doesn't turn on. so i had to cut the power supply and then turn it on again and after that it booted up.nothing is showing on the monitor.
in other words it doesn't restarted but i didn't worried much but now its worth it.
its been 2 days now and whenever i turn on my pc, lights show up but doesn't boot up.
let me briefly explain you...
there are 2 lights on CPU,one light have the symbol of light bulb and the other has a symbol of some sort of container with a line in the middle.
so when the pc starts normally the lightbulb's light is constantly turn on and the container light coonstantly flashing.but when it doesn't boot up,only the lightbulb's light is turn on,not the container one.
when i forcly shut down the CPU it doesn't whereas as i hold the power button the container light turns on with it and when i released the button it turns off.
the DVD room is getting out and in perfectly but not turning on.
now most of the time the PC doesn't boot up and right now i got the chance to publish this post.
ANY LIFE SAVER THERE??? PLEASE HELP ME.(it was important to briefly explain all this*)
remeber no beeping sound,anything else no...just all this.