Unable to open Synaptic, Update Manager or Package Manager

[8AfterMint]

Hi all,
I couple of day ago , I changed both my apt.config and my bashrc files to work my university proxy and has since restored them. Since then I have not been able to open the above-method programs. There are no error messages they just don't start. If I open Synaptic via the terminal I receive the follow error message:

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E: Could not open file /var/cache/apt/pkgcache.bin - open (2: No such file or directory)
E: _cache->open() failed, please report.

as well as this in the terminal

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(synaptic:7643): GLib-GObject-CRITICAL **: g_object_set_data: assertion `G_IS_OBJECT (object)' failed

(synaptic:7643): GLib-GObject-WARNING **: invalid (NULL) pointer instance

(synaptic:7643): GLib-GObject-CRITICAL **: g_signal_connect_data: assertion `G_TYPE_CHECK_INSTANCE (instance)' failed

if I try to open mintinstall via the terminal

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usr/lib/python2.7/dist-packages/gtk-2.0/gtk/__init__.py:57: GtkWarning: could not open display
  warnings.warn(str(e), _gtk.Warning)
Traceback (most recent call last):
  File "/usr/lib/linuxmint/mintInstall/mintinstall.py", line 28, in <module>
    from widgets.pathbar2 import NavigationBar
  File "/usr/lib/linuxmint/mintInstall/widgets/pathbar2.py", line 1025, in <module>
    class PathBarThemeHuman:
  File "/usr/lib/linuxmint/mintInstall/widgets/pathbar2.py", line 1038, in PathBarThemeHuman
    animate = gtk.settings_get_default().get_property("gtk-enable-animations")
AttributeError: 'NoneType' object has no attribute 'get_property'

Please help! it is very urgent.

Thanks

[bigj231]

So you can't use apt-get either? I guess you could try using dpkg to reinstall the apt components, but I don't know if that will work. Make a backup and start trying different things. A reinstall might be easiest though.