ubuntu 12.04 freezes up very frequently

I do not know the cause but the system freezes up in Firefox dash and synaptic
Already tried finding answers on the internet but encounter too many system failures

best regards
Wim Faasen

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: xorg 1:7.6+12ubuntu1
ProcVersionSignature: Ubuntu 3.2.0-26.41-generic-pae 3.2.19
Uname: Linux 3.2.0-26-generic-pae i686
NonfreeKernelModules: nvidia
ApportVersion: 2.0.1-0ubuntu8
Architecture: i386
Date: Thu Jul 12 19:38:41 2012
DistroCodename: precise
DistroVariant: ubuntu
InstallationMedia: Ubuntu 12.04 "Precise" - Build i386 LIVE Binary 20120427-09:21
ProcEnviron:
 PATH=(custom, no user)
 LANG=nl_NL.UTF-8
 SHELL=/bin/bash
SourcePackage: xorg
UpgradeStatus: No upgrade log present (probably fresh install)