You could try this reg file. Check if the path corresponds to your installation of WinRar.
---------------------------------------------------
Windows Registry Editor Version 5.00
[HKEY_CLASSES_ROOT\WinRAR\DefaultIcon]
@="C:\\Program Files\\WinRAR\\WinRAR.exe,0"
[HKEY_CLASSES_ROOT\WinRAR.REV\DefaultIcon]
@="C:\\Program Files\\WinRAR\\WinRAR.exe,1"
[HKEY_CLASSES_ROOT\WinRAR.ZIP\DefaultIcon]
@="C:\\Program Files\\WinRAR\\WinRAR.exe,0"
---------------------------------------------------