Windows XP Theme Reverted to Classic

For some reason my theme/style has reverted to classic
style/theme. I am running windows xp home, and now when I
go in the control panel or anywhere to change back to "xp
theme" that option is no longer listed in any of the drop
down menus. It is like I am not running xp, the only
options are classic, currrent theme (which is now classic)
or browse online? I heard that classic makes my computer
run a little fatsre, but I really like and want the
rounded edges and easy look xp has. What has happened? I
have restarted many times, checked all support docs. that
say things like xp style not supported for 64 bit systems,
which mine is not. I have no clue any ideas or
suggestions, please help. Thanks.

Dale