How can i play high quality games in windows 7 ?

i have 2gb ram, nvidia geforce 9400 gt which got 1gb video memory (ddr2). when i use windows xp some of my high quality games run smoothly but after upgrading my system into windows 7 they are not working. sometimes trying to run some games causes immediate crash (maybe blue screen). but the low system required games work correctly. is there any way to play high system required games in windows 7 smoothly like windows xp. my windows 7 is home basic (32 bit), processor is Pentium dual-core E5200 @ 2.50GHz 1.90GHz . 1 more thing i also want to know why this kinds of problem occur