thanks for all your help.
I have another problem,why my system running so slow?just now I right click and no response,terminal window shows up about 1 minute later.system became unuseable,I have to press power button to power off.I never came across this before
I play steam games just now,but keyboard not working,I cannot move in game.I press power button power off.I cannot go into system after reboot.So I go into bsd,but it's too stuck.I type reboot in terminal,but it didn't reboot,I have to press power button to poweroff.I cannot goes into neither system now.
I can boot to the GUI login,but very slow,and the system very stuck.I think there is something wrong with my hard disk.My ubuntu also went into problem a few days ago.My hard disk has a bad sector,msybe this cause the problem?I'll check my hard disk.