System restore can have an adverse effect on avast.
Having two resident anti-virus scanners installed is one too many and not recommended as rather than provide twice the protection it can cause conflicts that could leave you more vulnerable.
So once you resolve the MSE being installed.
If you still can't update - Try a Manual update of VPS -
avast! Virus Definitions Update - Manual Download VPS Update (virus definitions, vpsupd.exe, approx 31MB). - Save the file to your hard disk, locate where you saved it and double click it and that should carry out the virus definitions update.
Note: Ignore the file name in the images of the page that is displayed after clicking the download link, they are for the main program, not for vpsupd.exe which will be downloaded.