Connect a Keyboard to the Raspberry PI, and change the TTY (Terminal) in order to switch from the GUI to a Shell
This should give you a login prompt. Login with your user and uninstall the skins or reconfigure to use a default skin.
Note: This terminal will be a shell (Command Prompt), so you will have to determine the commands needed to uninstall or configure skins.
Linux Kernel has a certain number of "default terminals" (tty), typically this number is 7.
By convention the system boots and the GUI runs on
tty7. The "X Window System" (GUI) runs inside this terminal.
However, the other terminals 1-6 are still available to be used for other purposes. Sometimes these can be used to running multiple GUI Sessions, but they can also be used to recover the GUI system
The standard keyboard-command to switch tty is
F7 will take you back to the GUI terminal (