I can't install anything or upgrade anything after power problem...

I can't install anything or upgrade anything. It started shortly after we had a power outage while installing a piece of software. Ever since the software centre has not been of any use to me, am stuck.

Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/aptdaemon/worker.py", line 968, in simulate
    trans.unauthenticated = self._simulate_helper(trans)
  File "/usr/lib/python2.7/dist-packages/aptdaemon/worker.py", line 1092, in _simulate_helper
    return depends, self._cache.required_download, \
  File "/usr/lib/python2.7/dist-packages/apt/cache.py", line 235, in required_download
    pm.get_archives(fetcher, self._list, self._records)
SystemError: E:I wasn't able to locate a file for the xpdf package. This might mean you need to manually fix this package.

ProblemType: Bug
DistroRelease: Ubuntu 11.10
Package: software-center 5.0.3.1
ProcVersionSignature: Ubuntu 3.0.0-12.20-generic 3.0.4
Uname: Linux 3.0.0-12-generic i686
ApportVersion: 1.23-0ubuntu3
Architecture: i386
Date: Wed Feb 29 03:08:38 2012
InstallationMedia: Ubuntu 11.10 "Oneiric Ocelot" - Release i386 (20111012)
PackageArchitecture: all
SourcePackage: software-center
UpgradeStatus: Upgraded to oneiric on 2011-12-27 (63 days ago)