Home Network Help Please

[#1]

Hi,
RE: Accessing another computer on my home network for printer sharing and
hard disc access.
I have just switched to Plusnet, four weeks ago and so far its been excellent but...
I have a minor problem with my home network.

Basically, in a nutshell;
I can access my desktop PC from my laptop if the desktop is connected to the router
with an ETHERNET CABLE but not if the desktop is connected to the router via WiFi.
ALTHOUGH the desktop can use the WiFi to access the Internet and email etc.
So the WiFi to router connection is working & its reliable. (89% signal strength)
Basically both PC work fine 'individually'.
This has only happened since I joined Plusnet and replaced
the router with the Plusnet supplied unit.
A Thompson TG585 v8 (8.2.7.8)
I had no issues with my old setup using a Netgear router
(non ADSL2+ but maybe with a firmware update but that is another storey).
Both my computers, a Desktop and a Laptop are successfully connected to
the router via WiFi,
Both can access email (send and receive), both can surf the Internet, FTP etc.
So basically my setup is working without any issue,
The only issue is getting the laptop to access the desktop using WiFi for
both connections and not WiFi for the laptop and Ethernet for the desktop
Any advice would be appreciated.
Thanks

My Setup
========

COMPUTER 1
Desktop PC connected to router via WiFi
Windows XP fully updated
HP Printer/scanner connecter via a USB cable
No problems accessing the Internet or email servers.
Kaspersky Internet Suite 2012 (KIS) installed but turned off
(exited not suspend) at the moment until I resolve the issue.
So the KIS software has no influence on this issue.

COMPUTER 2
Laptop PC connected to router via WiFi
Windows XP fully updated
No problems accessing the Internet or email servers.
Kaspersky Internet Suite 2012 (KIS) installed but turned off
(exited not suspend) at the moment until I resolve the issue.
So the KIS software has no influence on this issue.

[#2]

Kaspersky Internet Security regards all wireless connections as belonging to public networks unless you tell it otherwise.  So it will block access to other network devices.  Possibly you found this problem and changed the settings appropriately for your old router but now you have a new one KIS has noticed this and gone back to its old obstructive ways.  You may think you have turned it off but it's not that easy unless you completely uninstall it - it is probably still running enough in the background to block the networking..

[#3]

Thanks for the advice.
I went into both Kaspersky programs;
one on the laptop and the one on the desktop
I set both of the WiFi to home network
I left the internet side to Public.
it started working so I thought great.
But this evening I couldn’t connect again.
I tried lots of time with no success then suddenly it is now all working again.
I don’t know if I have somehow changes something.
I will try again tomorrow and see if it still works.
I have just rebooted both machines (full power down and powered back up again)  and it is still working.
Possible it's fixed but I am not too confident about that.
it seems a bit temperamental
Could new router be faulty?
Could it be interference form one of my neighbours WiFi adapters, he seems to have lots of WiFi things, games, music senders,  'stuff'. Maybe he's gone to bed and turned off some stuff. A bit of straw clutching here.
it all seems a bit odd
As i said I will try again tomorrow and see if it still works.
thanks for the feedback.

[#4]

Some routers can be set up to isolate clients or groups of clients so they cannot see each other but that is a special feature which has to be explicitly turned on.  Otherwise if your computer can see the internet then the router will allow it to see all other connected computers.  I don't see that there is any possible router fault that could prevent this from happening so I'm sure this is NOT a router problem. 

[#5]

thanks for this information.
I will check to see if it is still working tonight and report back.
thanks again