Your overclock was too aggressive for your modules.
It isn't that easy to simply change the frequency and expect your RAM to work. It's like the CPU. If you want to find the best clock speed for your RAM, do it slowly. Try adding 5-10 MHz to the clock and see if it works. Do it until you start receiving errors.
To get your computer up and running again, just clear the CMOS memory. When your computer is off, push the CMOS reset switch if you have one. Otherwise, remove the CMOS battery. It's a small button cell battery. Wait for around 1-2 minutes then put it back in.
On a side note, I suggest you don't overclock RAM at all. The performance benefits are minimal at best.
there are also a jumper for resetting CMOS, look it up in your mobo manual. basically you turn off the computer, switch the jumper to reset, pull the CMOS battery (you can also hold down the power button to discharge capacitors), put the battery back in, switch the jumper back, then power the PC back up.
Also not when we say turn off the PC you should turn off the power supply switch at the back and unplug the power supply