my PC is on a small office network, and runs a server. The
internet is working fine on the PC, I can ping other
computers, and the IP address is correct (it's static), with
router and subnet IPs exactly the same as the other
computers in the network. However, I cannot ping my PC
from any of the other computers in the network, and
cannot connect to the server from other computers.

Yesterday I was having problems mapping a drive from
another computer on the network on the PC, so I went
through the network mapping tool, and used the network
connections wizard to reestablish the workgroup. I also
restarted the computer a couple of times. The drive
mapping problem is now fixed, but the ping problem
started while I was attempting to fix it.
I didn't change any of the firewall settings from their
previous state when the connection was working.

Thanks for your help

Have you tried disabling the Firewall temporarily?

Life is more painless for those who are brainless.