My linux machines were working fine until yesterday. I rebooted the machines and now I cannot mount disks across the net. I do not have a firewall.

"rpcinfo -u server nfs" returns
program 100003 version 2 ready and waiting
program 100003 version 3 ready and waiting

"rpcinfo -p" returns
program vers proto port
100000 2 tcp 111 portmapper
100000 2 udp 111 portmapper
100024 1 udp 32768 status
100024 1 tcp 32768 status
100021 1 udp 32769 nlockmgr
100021 3 udp 32769 nlockmgr
100021 4 udp 32769 nlockmgr
391002 2 tcp 32769 sgi_fam
100011 1 udp 812 rquotad
100011 2 udp 812 rquotad
100011 1 tcp 815 rquotad
100011 2 tcp 815 rquotad
100003 2 udp 2049 nfs
100003 3 udp 2049 nfs
100005 1 udp 32770 mountd
100005 1 tcp 32770 mountd

The "rpcinfo -p" returns
program vers proto port
100000 2 tcp 111 portmapper
100000 2 udp 111 portmapper
100024 1 udp 32768 status
100024 1 tcp 32768 status
100021 1 udp 32769 nlockmgr
100021 3 udp 32769 nlockmgr
100021 4 udp 32769 nlockmgr
391002 2 tcp 32769 sgi_fam
100011 1 udp 812 rquotad
100011 2 udp 812 rquotad
100011 1 tcp 815 rquotad
100011 2 tcp 815 rquotad
100003 2 udp 2049 nfs
100003 3 udp 2049 nfs
100005 1 udp 32770 mountd
100005 1 tcp 32770 mountd
390113 1 tcp 7937

Any suggestions?

Have you tried mounting the shared directory directory(ies) manually? Also have you checked the log files for any clues?