i need some help

hi guys,ive just bought a new cpu and mobo,and 2gig memory,the cpu is amd 64x2 4600,and the mobo is asrock am2nf3-vsta,the memory,i cant remember off hand,my graphics card is an old radeon 9800 pro,which is why i bought the mobo as it has agp slot(i cant afford a new card atm as im strapped for cash,and its only to play world of warcraft anyway)my psu is a jeantech ap500,i reinstalled windows,updated it,installed mobo drivers,got the latest cat drivers,and everything seemed ok,it runs fine,the problem occurs when i run my game,after 20 mins i get a blue screen with no writing on it,i thought it was maby a heat problem,but ive left the side off and ran a large desktop fan into the case,which doesnt make any differance,also when i run the game,i set up the graphics settings(in game) after it crashes the settings are back to default,ive tried using older catyalst drivers,with the same results,my old mobo is also asrock,k7 upgrade 600 and an amd xp2100 cpu,which ran the game fine using the same agp card and psu,any help would be great,thanks in advance