Some handy commands when it comes to refreshing a site to site vpn that has stopped working.
show isakmp sa - Displays the current status of ISAKMP SAs
show crypto ipsec sa - Displays the current status of IPSec SAs-useful for ensuring traffic is being encrypted
clear crypto isakmp sa – Clears ISAKMP SAs
clear crypto ipsec sa – Clears IPSec SAs
debug crypto isakmp – Displays ISAKMP (IKE) communications between the PIX Firewall and IPSec peers
debug crypto ipsec - Displays IPSec communications between the PIX Firewall and IPSec peers