boot in to safe mode by pressing F8 at the time of booting, then in safe mode readjust the refersh rate back to what it was earlier, in ur case it should be less than 70.
But I just noticed that u mention LCD....if thats the cas then LCD does not allow u to chnage that at all how did u change that refersh rtae.
If you just changed resolution than in safe mode change it back what it was earlier, than boot in normal mode.