Except if you insert special routing rules, you can't ping or access a host on a different subnet (I suppose your netmask is 255.255.255.0). Change the IP of proxmox, the one you gave it during installation is WRONG, is has to begin with 192.168.1.x and NOT 192.168.100.x, otherwise you can't access from other hosts.
So you think that proxmox IP is 192.168.1.4, but is 192.168.100.2. Also you tell about "eth0", don't touch it, is vmbr0 to config, but was done automatically during installation.
Since you messed things up, do this:
Log from console in proxmox (user root, password the one you provided during installation).
With an editor you are able to use edit the file /etc/network/interfaces and change the line so you will have ONLY something like this:
Code:
auto lo
iface lo inet loopback
iface eth0 inet manual
auto vmbr0
iface vmbr0 inet static
address 192.168.1.4
netmask 255.255.255.0
gateway 192.168.1.1
bridge_ports eth0
bridge_stp off
bridge_fd 0
save and exit.
reboot proxmox (command "reboot" from root prompt)
Enjoy, it will work