n10j problem...help

n10j vista ver.  I had downgrade it to xp every driver was install and working fine....but the mon will turn black suddenly sometimes(even i just open a folder, no other program running), but it doesnt mean that the system had hang....i can restart the computer with the keyboard then the screen is normal again but this problem with come up from time to time..... i had set 'never' on power management......and the power is not low..... any brother had this problem??