It could be an IP addressing issue. The Belkin Router's IP address will almost certainly be 192.168.2.1 and so the network drive needs to have an address in the same Subnet, i.e. a 192.168.2.x address. If it gets its address automatically from the Router by DHCP, then this should be OK but, if its address has to be configured manually, it needs an address that isn't already in use between 192.168.2.2 and 192.168.2.254, with the Subnet Mask address of 255.255.255.0
When your mate installed it with his Router, it is possible that it just happened to use the same Subnet as the Router, possibly 192.168.0.x or 192.168.1.x, which are more commonly used Subnets than Belkin's 192.168.2.x - not that that's a problem, I run my network with 192.168.5.x addresses.