Indeed. My recommendation is to go into Add/Remove Programs, uninstall anything with Java in its name, reboot, then download a fresh copy of java 7 or 8 if you feel like it appropriate for your architecture. Hopefully this isn't a completely corrupted install.
My first thought is that the chunk or region containing your base was somehow corrupted, resulting in Minecraft regenerating the area. It looks different because each new version brings about different terrain generation which in turn makes it so the same seed generates different content in the same spot based on game version.
Unfortunately, I would personally just chock this up to snapshots being buggy. When updating to a snapshot, back everything up. They're not marked as a proper release build for a reason; they have problems aplenty. Hopefully in the future things go better for you and your bases
To answer your other question about getting things back - unless you had a backup, very unlikely :/
Edit, one more thing. If you use MCEdit or a similar program (http://mcedit.net) to delete that specific chunk, then load up the version you first joined the world with, Minecraft should regenerate the chunk with the proper terrain features and biome, as it was when you first joined. Be wary, MCEdit has huge destruction potential. Make backups
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Unfortunately, I would personally just chock this up to snapshots being buggy. When updating to a snapshot, back everything up. They're not marked as a proper release build for a reason; they have problems aplenty. Hopefully in the future things go better for you and your bases
To answer your other question about getting things back - unless you had a backup, very unlikely :/
Edit, one more thing. If you use MCEdit or a similar program (http://mcedit.net) to delete that specific chunk, then load up the version you first joined the world with, Minecraft should regenerate the chunk with the proper terrain features and biome, as it was when you first joined. Be wary, MCEdit has huge destruction potential. Make backups
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