Lets hope you did not format your linux operating system.
In that case apart from what vinaytp suggested, if you have multiple disks then also try
grub > root (hd1,0)
grub > root (hd1,1)
Which will search for a linux partition of second disk (order set according to BIOS). If it finds a valid partition (i.e. when the above command is successful, you can try to find out the kernel and boot using
grub > kernel /boot/vmlinuz[hit tab here, if you find a kernel hit enter]
grub > initrd /boot/initrd[[hit tab here, if auto-completes hit enter]
grub > boot
Hopefully, you will have your system booted.