Just confirm your Avast build (version) is in fact 4.8.1368? (At this time, that's the current one.)
I would think that some kind of conflict with WD is possible, but others run the combo OK..maybe it's the low RAM/CPU exacerbating it?
It would not hurt to try a full reinstall of Avast. Check first that there are no files in the infected or user section of the chest that you may want. Make sure a copy of your license has been kept. (This would have been emailed to you after your initial install of Avast, and re-sent (on request) every 14months. ) I'd leave WD disabled while you do this.
-Download the full Avast file setupEng.exe from
here. Do not download the universal setup file. The file you download should be ~39Mb.
-Download the Avast uninstall utility from
here.-Go offline. Stop on access protection. Go to "program settings>troubleshooting" and disable the self protection module.
-Uninstall Avast from the control panel. Reboot. If there were any problems, reboot into safe mode.
-Run the uninstall utility. Reboot.
-Install Avast using the new setup file. Reboot if prompted. You may opt out of doing the boot scan..it takes quite a while, and is appropriate for new users of Avast, or where an infection is suspected.
-Reconnect. Get updates. Let us know if it helps or makes any difference.