The options are going to depend on your situation. Do you have two separate source trees as where the kernels were compiled? If so, the
.config file in the top level directory of the source will reflect the configuration.
If I had to guess without enough details, I'd suggest that you may not have selected the appropriate drivers for the disk controllers.
On the kernel that boots, if the necessary options are compiled, you can reference /proc/config.gz. Unfortunately, this will not help you much as one of the kernels will not boot. Nevertheless, it could help to compare what is compiled on the working kernel, however, and you could update the broken configuration accordingly.
Certain distributions include the config for the compiled kernel with the package and put it in /boot.
 These options: