That's exactly what mine did and i ended up needing a new motherboard (chipset fried)
It could be a number of things though, so start with the basics and troubleshoot your way through.
First i would suggest to try one stick of memory at a time (if you have 2 of course )... Then reseat the video card, or try a different card if you have a spare.
If it still doesn't boot, then unplug everything from the back of the system and unplug all drives inside the system and try it again..
If still no joy then also take out any extra cards and leave just the memory and graphics card installed...
After that if it still doesn't work, i would say its doubtful to be the memory if you tested 2 sticks, so that narrows it down to the motherboard cpu and graphics card, the more likely ones being the graphics card or motherboard !
Great if you have a mate with similar system then you can test their parts etc in yours
