dell xps 420 boot up issue

Heya all, I'm trying to fix my moms pc for her, most times i can get it, but this has me stumped, she has a dell xps 420 desktop, a few days ago she tried to turn it on, and the power light was a constant yellow with a sound like the fan was trying to turn, no smells or anything, I followed the various steps, unplugging everything, started it up, 1,3,4 flashed on top, with the power button flashing yellow/blue and the fan sounded like it was trying to rev for a race, then the little screen said no memory detected (I had the memory cards out at this point), reinstalled them, restarted, 1,3,4, same flash pattern, then at the end it said 3,4 memory cards detected but not working, so I then put the video card back in, and it screamed bloody murder at me, turned it off, took out the video card, did a beep code this time, by the sounds of it, the same as for the memory card, so, my question is,  1,3,4 suggests a mobo failure, would i be better off ordering a new one, or should i try something else? thanks!