症状是：
1. 每次启动 xp 时，滚动条跑到一半就自动重启。
2. 每次启动ubuntu 时，跑完进度条后是黑屏。一直没有反应，只能按重启键重启，然后一切正常。
3. 应该不是内核的问题，因为我已经用了好几个内核了，都有这个问题。
系统日志里我按重启键前的最后几条是：
Aug 2 19:18:12 mike-desktop avahi-daemon[4903]: Successfully called chroot().
Aug 2 19:18:12 mike-desktop avahi-daemon[4903]: Successfully dropped remaining capabilities.
Aug 2 19:18:12 mike-desktop avahi-daemon[4903]: No service file found in /etc/avahi/services.
Aug 2 19:18:12 mike-desktop avahi-daemon[4903]: Network interface enumeration completed.
Aug 2 19:18:12 mike-desktop avahi-daemon[4903]: Registering HINFO record with values 'I686'/'LINUX'.
Aug 2 19:18:12 mike-desktop avahi-daemon[4903]: Server startup complete. Host name is mike-desktop.local. Local service cookie is 1058083400.
Aug 2 19:18:12 mike-desktop kernel: [ 47.690229] apm: BIOS version 1.2 Flags 0x07 (Driver version 1.16ac)
Aug 2 19:18:12 mike-desktop kernel: [ 47.690234] apm: disabled - APM is not SMP safe.
Aug 2 19:19:10 mike-desktop syslogd 1.5.0#1ubuntu1: restart.
请问大家这是什么原因？ 谢谢你们！
