Can you test this?

Select START > RUN …
Enter the following command:
C:\WINDOWS\SysWOW64\REGSVR32.EXE ACTSKIN4.OCX

Press OK (or Enter).
A message saying that the file was successfully registered should appear…

If that does not work, seems that for some reason, ActiveSkin (the 3rd party library avast uses for skinning) does not seem to be working on your system. As a workaround, we may disable skinning in avast - that should solve the problem. To do that, open the file \data\avast4.ini, look up the [UserInterface] section, and add the following entry:

StartWithSkin=0