[ubuntu] up down not moving in gnu grub version 1.99 12ubuntu5.1 dual boot

Hi

I have dual OS win-7 and ubuntu 11.10 in my system. Every thing was fine but suddenly up and down arrow not moving to select the option in grub screen. Means now I am not able to select the windows7 or memory test and so on...........Please help me to solve this

Thanks in Advance