Hi arcturus,
Welcome to the fun house.
Messing about with your setup is half the fun. Keep on doing it, but backup things.
The item Galen mentions will get back all your user desktops to pristine condition.
Or for more fun fire up a konsole terminal and obliterate the hidden dot file .kde4. It will recreate itself but will be a default .kde4 desktop, not PClinuxOS. To get that go with Galen.
Next having your desktop back start messing with it again, EXCEPT:
Back to terminal konsole.
Backup .kde4 to say .kde4bak (Command is cp -a .kde4 .kde4bak)
Remember to back up your desktop from time to time.
After messing with your desktop and getting it into a really terrible state:
Back to terminal konsole.
I find you have to obliterate .kde4, and I tend to do it as root, so care:
make sure you are in your home directory
su
(roots passwd)
rm -rf .kde4 (that is that obliterated)
cp -a .kde4bak .kde4
Log back in. I tend to be logged out of the user desktop when doing this.
Note you have virtual terminals Ctrl +Alt+F1-7 with F8 or F9 being the desktop.
Alternative is to use a new Activity. Right click the desktop, see if you have a spare activity or create a new one, make sure you do not mess with your main desktop. mess around with a different activity.
Knowing how to recover your desktop gives you peace of mind. Protecting your perfect desktop is strongly recommended.