Network Problem

[dandan556]

Hello, i have a small network problem in which i cant access PC2 from PC3 and visa versa, they cant contact each other in anyway, all the PC's can be seen in the same workgroup from each PC, all this will become clear in the diagram below.

The green arrows indicate the PC's that can talk to each other (eg. ping each other), and the red arrow the PC's that can not.

I'm not very good at explaining things, if you require any more info just gimme a shout.

Thanks in advance.

 

[dandan556]

Firewalls?
Can the machines that can't ping each other ping the router?

No firewalls running, they can all ping the router, access the internet etc..
Just PC3 and PC2 that cant talk to each other, in a computing way of course