Alienware X51 not turning on

Hey all,

I logged into ESO last night, got up to get a drink and when I came back my computer was powered down and the little power saving light was dim. I pushed the power button and nothing happened. If I hold the power button down the power light goes completely off. Looking for information on what to do? I've read it might be the mother board went out if that's the case would it be easier to buy and replace or get a new pc all together? Any help is appreciated.