服务器崩溃后 MongoDB 无法启动

我的Ubuntu电脑崩溃了，当我重新启动它时，MongoDB无法工作.我try 了以下命令，得到了以下输出:

$ mongo
Error: couldn't connect to server 127.0.0.1:27017 src/mongo/shell/mongo.js:91
exception: connect failed

$ service mongodb status
mongodb stop/waiting

$ service mongodb restart
stop: Unknown instance: 
start: Rejected send message, 1 matched rules; type="method_call",
       sender=":1.57" (uid=1000 pid=2227 comm="start mongodb ")
       interface="com.ubuntu.Upstart0_6.Job" member="Start" error name="(unset)"
       requested_reply="0"
       destination="com.ubuntu.Upstart" (uid=0 pid=1 comm="/sbin/init")

$ tail /var/log/mongodb/mongodb.log
[initandlisten] exception in initAndListen: 12596 old lock file, terminating
dbexit: 
[initandlisten] shutdown: going to close listening sockets...
[initandlisten] shutdown: going to flush diaglog...
[initandlisten] shutdown: going to close sockets...
[initandlisten] shutdown: waiting for fs preallocator...
[initandlisten] shutdown: closing all files...
[initandlisten] closeAllFiles() finished
dbexit: really exiting now

(输出重新格式化以匹配网站布局.)

怎么搞的？我该怎么修？