我安装了 Ubuntu，想删除 Python 3。我意外地删除了所有已安装的 Python 版本，因为我不知道 Ubuntu Desktop 需要 Python 才能运行。我不得不完全重新安装 Ubuntu（我几乎没有任何文件）。但现在启动时我的 PC 卡在紫色屏幕。我强制关闭它并重新启动它。出现 Memtest 和高级选项的屏幕，我选择 Ubuntu，然后它会简要检查一些块并按预期启动。我不想每次都重复这个过程。你知道是什么原因导致这些问题吗？是 GRUB 的问题吗？我有一台戴尔 Inspiron 5300 塔式机。
更新：
这是我的lightdm.log文件：
[+0.02s] DEBUG: Logging to /var/log/lightdm/lightdm.log
[+0.02s] DEBUG: Starting Light Display Manager 1.16.4, UID=0 PID=650
[+0.02s] DEBUG: Loading configuration dirs from /usr/share/lightdm/lightdm.conf.d
[+0.02s] DEBUG: Loading configuration from /usr/share/lightdm/lightdm.conf.d/50-greeter-wrapper.conf
[+0.02s] DEBUG: Loading configuration from /usr/share/lightdm/lightdm.conf.d/50-guest-wrapper.conf
[+0.02s] DEBUG: Loading configuration from /usr/share/lightdm/lightdm.conf.d/50-ubuntu.conf
[+0.02s] DEBUG: Loading configuration from /usr/share/lightdm/lightdm.conf.d/50-unity-greeter.conf
[+0.02s] DEBUG: Loading configuration from /usr/share/lightdm/lightdm.conf.d/50-xserver-command.conf
[+0.02s] DEBUG: Loading configuration dirs from /usr/local/share/lightdm/lightdm.conf.d
[+0.02s] DEBUG: Loading configuration dirs from /etc/xdg/lightdm/lightdm.conf.d
[+0.02s] DEBUG: Loading configuration from /etc/lightdm/lightdm.conf
[+0.02s] DEBUG: Using D-Bus name org.freedesktop.DisplayManager
[+0.02s] DEBUG: Registered seat module xlocal
[+0.02s] DEBUG: Registered seat module xremote
[+0.02s] DEBUG: Registered seat module unity
[+0.03s] DEBUG: Monitoring logind for seats
[+0.03s] DEBUG: New seat added from logind: seat0
[+0.03s] DEBUG: Seat seat0: Loading properties from config section Seat:*
[+0.03s] DEBUG: Seat seat0: Starting
[+0.03s] DEBUG: Seat seat0: Creating user session
[+0.03s] DEBUG: Loading users from org.freedesktop.Accounts
[+0.03s] DEBUG: User /org/freedesktop/Accounts/User1000 added
[+0.08s] DEBUG: Seat seat0: Creating display server of type x
[+0.09s] DEBUG: Deactivating Plymouth
[+0.11s] DEBUG: Using VT 7
[+0.11s] DEBUG: Seat seat0: Starting local X display on VT 7
[+0.11s] DEBUG: DisplayServer x-0: Logging to /var/log/lightdm/x-0.log
[+0.11s] DEBUG: DisplayServer x-0: Writing X server authority to /var/run/lightdm/root/:0
[+0.11s] DEBUG: DisplayServer x-0: Launching X Server
[+0.11s] DEBUG: Launching process 662: /usr/bin/X -core :0 -seat seat0 -auth /var/run/lightdm/root/:0 -n$
[+0.11s] DEBUG: DisplayServer x-0: Waiting for ready signal from X server :0
[+0.11s] DEBUG: Acquired bus name org.freedesktop.DisplayManager
[+0.11s] DEBUG: Registering seat with bus path /org/freedesktop/DisplayManager/Seat0
[+0.55s] DEBUG: Got signal 10 from process 662
[+0.55s] DEBUG: DisplayServer x-0: Got signal from X server :0
[+0.55s] DEBUG: DisplayServer x-0: Connecting to XServer :0
[+0.55s] DEBUG: Quitting Plymouth; retaining splash
[+0.57s] DEBUG: Seat seat0: Display server ready, starting session authentication
[+0.57s] DEBUG: Session pid=669: Started with service 'lightdm-autologin', username 'steve'
[+0.60s] DEBUG: Session pid=669: Authentication complete with return value 0: Success
[+0.60s] DEBUG: Seat seat0: Session authenticated, running command
[+0.60s] DEBUG: Registering session with bus path /org/freedesktop/DisplayManage/Session0
[+0.61s] DEBUG: Session pid=669: Running command /usr/sbin/lightdm-session gnome-session --session=ubuntu
[+0.61s] DEBUG: Creating shared data directory /var/lib/lightdm-data/steve
[+0.61s] DEBUG: Session pid=669: Logging to .xsession-errors
[+0.84s] DEBUG: Activating VT 7
[+0.84s] DEBUG: Activating login1 session c1
[+0.84s] DEBUG: Seat seat0 changes active session to c1
[+0.84s] DEBUG: Session c1 is already active
这是我的x-o.log文件：
X.Org X Server 1.17.2
Release Date: 2015-06-16
X Protocol Version 11, Revision 0
Build Operating System: Linux 3.19.0-30-generic x86_64 Ubuntu
Current Operating System: Linux ubuntu-x64-steve 4.2.0-16-generic #19-Ubuntu SMP Thu Oct 8 15:35:06 UTC 2015 x86_64
Kernel command line: BOOT_IMAGE=/boot/vmlinuz-4.2.0-16-generic root=UUID=1ce2943d-991b-4263-9d84-34617abe91f1 ro quiet splash
Build Date: 30 September 2015 09:08:47AM
xorg-server 2:1.17.2-1ubuntu9 (For technical support please see http://www.ubuntu.com/support)
Current version of pixman: 0.32.6
Before reporting problems, check http://wiki.x.org
to make sure that you have the latest version.
Markers: (--) probed, (**) from config file, (==) default setting,
(++) from command line, (!!) notice, (II) informational,
(WW) warning, (EE) error, (NI) not implemented, (??) unknown.
(==) Log file: "/var/log/Xorg.0.log", Time: Tue Nov 3 17:13:09 2015
(==) Using system config directory "/usr/share/X11/xorg.conf.d"
我知道这有点混乱，但我不知道如何做得更好。.old.log这些文件也有版本，你需要吗？