装了ubuntu14.04lts,总是遇到死机的情况，不知道怎么回事？

[freestyle4568]

有的时候看视频看的好好的死机了，有的时候浏览网页死机了。
以前在用12.04的时候没有出现过这种情况，不知道怎么回事，求助各位。
这是我的syslog中的内容：（都是红字出现的）
3068 Oct 10 22:30:02 freestyle4568-Lenovo kernel: [ 15.925808] nvidia: module verification failed: signature and/or required key missing - tainting kernel
3080 Oct 10 22:30:02 freestyle4568-Lenovo kernel: [ 16.229069] b43: probe of bcma0:0 failed with error -524
3097 Oct 10 22:30:02 freestyle4568-Lenovo kernel: [ 16.621313] systemd-udevd[485]: failed to execute '/usr/sbin/alsactl' '/usr/sbin/alsactl -E HOME=/var/run/alsa restore 0': No such file or directory
3098 Oct 10 22:30:02 freestyle4568-Lenovo kernel: [ 16.623344] systemd-udevd[486]: failed to execute '/usr/sbin/alsactl' '/usr/sbin/alsactl -E HOME=/var/run/alsa restore 1': No such file or directory
3140 Oct 10 22:30:04 freestyle4568-Lenovo bluetoothd[878]: Failed to init deviceinfo plugin
3141 Oct 10 22:30:04 freestyle4568-Lenovo bluetoothd[878]: Failed to init proximity plugin
3142 Oct 10 22:30:04 freestyle4568-Lenovo bluetoothd[878]: Failed to init time plugin
3143 Oct 10 22:30:04 freestyle4568-Lenovo bluetoothd[878]: Failed to init alert plugin
3144 Oct 10 22:30:04 freestyle4568-Lenovo bluetoothd[878]: Failed to init thermometer plugin
3140 Oct 10 22:30:04 freestyle4568-Lenovo bluetoothd[878]: Failed to init deviceinfo plugin
3141 Oct 10 22:30:04 freestyle4568-Lenovo bluetoothd[878]: Failed to init proximity plugin
3142 Oct 10 22:30:04 freestyle4568-Lenovo bluetoothd[878]: Failed to init time plugin
3143 Oct 10 22:30:04 freestyle4568-Lenovo bluetoothd[878]: Failed to init alert plugin
3144 Oct 10 22:30:04 freestyle4568-Lenovo bluetoothd[878]: Failed to init thermometer plugin
3140 Oct 10 22:30:04 freestyle4568-Lenovo bluetoothd[878]: Failed to init deviceinfo plugin
3141 Oct 10 22:30:04 freestyle4568-Lenovo bluetoothd[878]: Failed to init proximity plugin
3142 Oct 10 22:30:04 freestyle4568-Lenovo bluetoothd[878]: Failed to init time plugin
3143 Oct 10 22:30:04 freestyle4568-Lenovo bluetoothd[878]: Failed to init alert plugin
3144 Oct 10 22:30:04 freestyle4568-Lenovo bluetoothd[878]: Failed to init thermometer plugin

[lhw828]

有定期更新系统吗？