TG582n FTTC - access to external hard drive

[#1]

Hi my fibre connection got activated yesterday am now struggling with trying to access my external hard drive via the router which is an issue I have not had before. I spoke to Plusnet's router support this morning who said they could not assist so here I am!
I have a Mac I am connected to the router via ethernet the external hard drive is connected to the router via ethernet. The steady green light on the hard drive suggests it is working fine. I cannot see the external hard drive in the left hand panel of 'finder' on my Mac. When I login into the router the hard drive is shown as being connected to my home network.
My initial thought was I needed to go through the hard drive set-up process again as my router had changed. I tried this but the software failed to recognise the external hard drive that the router tinks is connected to the router.
Help!

[#2]

Some further info .....
The external hard drive is WD My Book Live in the detailed manual it indicates how to access it via a browser - which am able to do. The manual suggests "certain network protocols may be blocked on the network or the computer" and that I should "check your local router for any firewalls or security software. If present, please check your router documentation on temporarily disabling the software or configuring the software to allow UPnP or UDP traffic".
Any thoughts on how to proceed as regards checking/sorting the router's settings?
Thanks any help.

[#3]

I am using Windows/iOS/Android and my MBL worked straight out of the box.  I have mine, and the ethernet PCs, plugged into a gigabit switch which is plugged into the router, The iOS and android devices access the MBL by WiFi through the router  I did not modify any settings on the router (in fact, the firewall settings are not available on the PN version). The MBL dashboard network setting is set to DHCP and, after it was connected, I set the IP addess to fixed on the Technicolor Home Network page.
First thoughts:
have you, by chance, set the MBL to a fixed IP address that is not within the range of the new router - shouldn't be, as you can see it on the router network map.
When you access the MBL through its webpage, does the settings-network page show a good connection with the correct IP.
It looks as though it's your MAC rather than the router or MBL, try accessing and mapping the MBL as a network drive from another PC on your LAN - that should sort out if it's the router or your MAC.

[#4]

Hi frank39 thanks for your reply you are quite right the problem is my Mac or to be more specific the OS X operating system. I noticed the external hard drive suddenly appeared in the list of share devices in 'Finder' then a few minutes later had disappeared. I did a 'Force Quit' and relaunched  'Finder' and the external hard drive re-appeared. A search of postings relating to 'Finder' on the internet came up with reports of issues with 'Finder' that Apple will hopefully have resolved by the time 10.8.2 comes out in the next few weeks or so!
I can now access the files on my external hard drive. Whilst I may in future access them via a different route than I did in the past that's not a problem!

[#5]

There were occasional issues with Vista over the transient appearance of network drives, they don't seem to appear in Win7. I found that mapping the drive, reconnecting at boot and allocating a drive letter improved things.  There are no grounds for thinking that anything about Windows applies to the Mac OS, but it must be worth a try.