Normally when mounting NFS it's a good idea to have flags set similar to this:

bg,intr,soft

bg      If  the  first  NFS  mount  attempt times out, retry the mount in the            background.  After a mount operation is backgrounded, all subsequent mounts           on the same NFS  server  will  be  backgrounded immediately, without first           attempting the mount.  A missing mount point is treated as a timeout, to           allow for nested NFS mounts.   soft    If  an  NFS  file operation has a major timeout then report an I/O error           to the calling program.  The default is to continue retrying NFS file           operations indefinitely.   intr    If  an  NFS  file  operation  has  a major timeout and it is hard mounted,           then allow signals to interupt the file operation and cause it to return           EINTR to the calling program.  The default is to not allow file operations           to be interrupted.

You can in addition set:

timeo=5,retrans=5,actimeo=10,retry=5