I lost my database in SQL server 2008 R2
You can try attaching the missing databases using the files. You can right click on the databases folder in Management Studio and select "Attach".

Another option, and the one I would generally go for, would be to use any backups you have. You will experience some data loss though.  If you are using the full recovery model for your databases, you should be able to restore to the last transaction log backup. Otherwise if you are using the simple recovery model you can only restore from the latest full backup.