Most likely the locking up was all the time due to your
a) Motherboard
b) Ram
Did you check your ram slots that they are absolutely sure seated properly? One comb even a little crooked may render the computer unbootable. Next remove all peripherals except cpu, main harddrive, ONE ram stick and displaycard. Try to boot up.
If it fails, change the memory stick to another and try again. Make sure that you reset your CMOS before trying the above just to make sure you didn't screw anything up in the settings.
If the above continues to fail it might be the motherboard or it might be displaycard or another broken device. Try booting up with only cpu , hd and ram next, if it beeps for 'post' then you have a displaycard problem.
Don't buy new hardware untill you've performed those steps.