Problem accessing a site.

Hi people,
I've got a strange problem where I can't connect to or ping a
particular machine on the internet. However, I can connect to "sister"
machine that is hosted at the same location. The machine I can't connect
to is x.x.x.9 and the machine I can connect to is x.x.x.10. Once sshed
onto x.x.x.10 and I can connect to x.x.x.9.

A tracert to x.x.x.9 gets as far as the firebrick infront of the
machine before a timeout connecting to x.x.x.9 - though I'm not sure
what this proves if I can't ping x.x.x.9 anyway.

A tracert to x.x.x.10 works fine - and gets passed the firebrick.

nslookups and reverse lookups work fine.

I've spoken to BTYahoo, my ISP, and they say there are no website
blocks on my account. BTYahoo can connect to x.x.x.9 machine OK.

I disconnected and reconnected my router so I got a new IP address.
Still no luck - so I am guessing that my IP isn't being blocked at host
site. Maybe my MAC address is?

Any ideas? I am completly stuck.

Cheers
James.

P.S. Sorry if this is a double post, but my earlier post doesn't seemed
to have appeared.