Did you have an earlier version of avast installed ?
If so a clean reinstall may be enough to resolve this, see #### below.
If it doesn't resolve it, it could be this:
There appears to be a conflict between the avast behaviour shield and some low level drivers including some by Dells, but this has tended to be the laptops. They are working on this and hopefully there will be a program update soon to resolve it.
Try reinstall avast, but do a clean, but custom install, this allows you to deselect components/shields and uncheck the Behaviour Shield and continue the installation.
This assumes you are using avast free.
####
- Download the latest version of avast, 5.1.864
http://files.avast.com/iavs5x/setup_av_free_eng.exe (English only) and save it to your HDD, somewhere you can find it again (if you didn't save your last download). Use that when you reinstall.
- Download the avast! Uninstall Utility, aswClear5.exe
find it here and save it to your HDD (it has uninstall tools for both 4.8 and 5.0).
- 1. Now uninstall avast! (using add remove programs, if you can't do that start from the next step), reboot.
- 2. run the avast! Uninstall Utility from safe mode, first for 4.8 if previously installed and then for 5.0, once complete reboot into normal mode.
- 3. install the latest version, reboot.