A few things I can think of. First, as Avevm suggested, try a different psu. If the psu is bad, nothing else can work properly. Next thing I would look at is the motherboard.
Of course, the whole name of this thread is strange. "Why you should build your own rig", and then you go on to tell how a Dell works properly? I mean, if the Dell works properly, then that is a reason to buy a ready built computer instead of build one. Maybe it would have been better to complain about ABS.