[URGENT] I lost my 400 GB partition, How to Recover Some data?

OK, calm down first. Don't do any operation on your drive now 'cause any wrong operation will cause data overwritten situation and once this happens, you will lose the chance to recover your files. Type data recovery on Google you will find many data recovery software that you can choose, make sure the one you choose will not do harm to your data (you can use a USB drive to try it first). There are paid software and freeware that you can choose, make sure the freeware will not bring you ads or virus, and also make sure the paid one offers the free scan option for you to see if it can find your files, then decide if you want to purchase it to recover your files. No matter what methods you choose, remember this carefully: DO NOT put any any any new files on your drive, I mean it. Good luck.

important files are supposed to to backed up regularly, so that you won't be bothered by data loss. now you can try partitionguru or eassos recovery free to searching for deleted files. good luck http://www.wikihow.com/Recover-Lost-Partitions