For NFS to run, you need to have the RPC daemons running. The two required daemons are rpc.portmap and rpc.statd. These are normally started at bootup time. If these are not running, you will not be able to mount NFS partitions. So you need to start them.

In Slackware, as root, you would go to /etc/rc.d and make rc.rpc executable and then

/etc/rc.d/rc.rpc start

In other distributions, you would look in your startup services, and turn on the RPC daemons, and then start them. Once your system has the RPC daemons running, then you will be about to mount your NFS partition.