Good to hear from you that is all ok. Let's go to your questions:
The first switch have in the display the leter C and the others too have the letter S.
Correct. The master switch shows in its display the letter C; the slaves shows the letter S.
My problem now is that can not ping the Stack IP using the command promt and also can´t access the web interface.
Which IP are you trying to ping? Remember that the IP address of the stack is assigned to the VLAN 1 interface and is only for the stack management purposes, this IP does not answer to ICMP requests from the network. The stack will use this IP to maintain the stack in operational status. Through the web console you can access the stack, but you have to reach an IP address assigned to another VLAN interface created in the whole stack - you need to create the same VLAN settings on the switches that belongs to the stack.
The only access to the switch´s is throught the Console Port.
Ok, this is related to what I wrote above. When you create a VLAN interface and assign an IP address to it you will be able to open the web console using this IP address.
Is this normal ? I have a 4 unit stack on my old SuperStack II 3300 and did not have these problems configurating it and access it.
Unfortunately, this is normal. The Device Manager (3com management software) cannot manage the stack as well. Actually the 4500G acts like a cluster, the advantage from a cluster is the faster convergence and some benefits when stacked.
Should i just use the clusted option the Web Interface ?
I don't use the web interface; I don't like it. I always use the SSH or telnet connections to manage the stack, and when I need to configure a slave switch all I have to do is enter that command:"stack switch-id to <member_id>.
HTH