Minecraft Biome / Spawnpoint shifted

Solution 1:

If the biomes shifted it's probably due to a corrupted "seed" (just a long number) which seems to happen quite easily when the server crash. If you have an old save that still is ok you can get the correct seed from that save, and then edit your current save and set the correct seed.

It's really easy to read and set seeds with LolEdit. You just open the save in the editor and modify the seed field.

If you have explored new areas while the seed was corrupted you might also get problems with "sliced walls". Check my slighty longish answer in this thread for a solution to that.