My computer has stopped booting up

hi i have recently put on a copy of windows xp onto my computer as i do not at the moment have time to buy windows 7. i installed the os at home and it worked fine then i put it in the car and move it to my student flat and it no longer starts up, all lights turn on but nohting comes up on screen i have tried it on another monitor and still doesnt work.
any help would be great thanks
the computer is a custom build
amd athlon II quad core
8gb ram
600watt psu
 
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