Sounds like your monitor did not accept the refresh rate.
That's not an overclock by the way your simply changing how fast your Monitor refreshes the screen rate.
Boot into safe mode and remove the program and best bet is to not mess with it anymore.
When you turn the PC on most OS use F8 to access the boot options. Spam that key till it brings you to a DOS screen and select Safemode with command prompt. Then let windows load and go uninstall that program.