Windows XP: Windows XP - unable to change visual style windows/buttons

Windows XP - unable to change visual style windows/buttons

Hi, I have been researching for quite some time now and have not been able to figure out why I cannot change my Windows XP SP2 visual style for windows and buttons from the "windows classic style". It is currently greyed out and inhibited for any change at all. I have edited my registry files (compared them with many correct ones) AND followed about 3-4 different options that microsoft offered on their site with no success. I have even attempted downloading a differnt style but was not able to get that to load/work either. Any opinions or fixes or anything at all to put me on the right track would be greatly appreciated. Thanks in advance for any help!