I am moving this thread to the Alienware Owners Club Forum.
 
Bev.

1. motherboard? power supply? oh, i also checked ram with tests and swapping out for old ram, same problem.   2. im starting to think the psu isnt supplying enough power to gpu. but i cant find a replacement and seems aftermarket is tricky?   3. any advice? please help, im stuck

1. Right ... or the piece you haven't replaced yet. 

2. Dell Spare Parts has them. Digital Power Supply Tester is only $25 at Newegg.

Assuming the power supply wire colors indicate the 12v rails going to the video cards:
Try with a power connector from each wire set at the same time.
Meaning, use either P14 OR P15
and also
either P16 OR P17

3. Since you don't have a motherboard laying around, you might have to move the pieces (video cards, ram, etc.) to a second machine ... see where the problems follow ... or be able to certify some parts are definitely good.

Thanks for the reply , i got a new power supply and seemed to work ok , but ten mins in back to the same problem. So defo not ram, Gpu Or psu. Does that leave the motherboard ? Could the processor be bust? Occasionally gettin beeps when computer crashes . Gettin one beep then a min or so later getting 5 beeps from mobo. Any advice appreciated :)

Could the processor be bust?

Yes, but unless it was abused or there was some event ... I would guess the motherboard.

By testing the way I said or on bench, you don't have to guess so much.