Open your registry and find the key below.
Create a new string value, or modify the existing value, called "Max Cached Icons" and set it to "8192". This will increase the icon cache to 8MB (8192kb).
Restart Windows for the change to take effect.
Key:[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer]
Value Name: Max Cached Icons
Data Type: REG_SZ
Data:8192
