trainz not accepting new pc

i recently upgraded my pc
intel core i3 3220
asrock b75m
gskill ripjaws 4gb
xigmatech utgard case
cooler master extreme series 460 watts psu
samsung dvd rw
gtx 550(from old pc)
seagate 500 gb hdd 32mb cache


whenever i run trainz my pc turn off after 5 mins and then restart.this happening only with trainz .i am playing maxpayne 3 need for speed the run ,la.noire,gta iv mafia 2 on highest settings.my pc handles it easily even after game play of 4 hours my pc never gave any problem also pc temps at max loads are cpu 40 and gpu 45 so no chance of over heating .so what do you think what the matter it can be .plz help me how to get rid of it

Have you run a full test of your ram? I use this free software utility: MEMTEST

I've seen machines that would crash when only specific programs were run and, more than once, it's required replacing a faulty memory module.