motherboard -gigabyte g 31
processor-intel core 2due 2.8 E7400
ram - 4gb DDR2
GPU-Sapphie readon hd 7730
my psu was with casing it has 450 wat
my all games lags..
when i start the game there is 55-60 fps
but when i start a mission it falls to 15-25
it happens every timecan any one help me plz.....