external drive probs with nforce 2 mobo

kk i use an external laptop drive and it simply freezes and locks up after a certain time with my abit nf7-s revision 2 mobo. it would be 5 mins one time, 20 the next, but no matter what it will lock up. i use two usb connectors so its not an underpower issue. anyone else experience this problem? i tried it on my bros pc and it works perfectly on his asus mobo.