Vista Network share problems

OK for the past 4-5 months I've had my 2 desktop's PC's networked via a Netgear router, both are running Vista Ultimate 32bit & everything's been perfect for these past 4-5 months.

Last night I removed a TV Card (WinTV Express) out of my main system (Computer A) & replaced it with a better card (PCTV Stereo). After doing that the file/printer sharing from Computer A became inaccesable from Computer B.

Computer A Can access eveything on Computer B just like before, however although Computer B can see Computer A in the network folder when i try to access it i get the error (\\computer is not accessible you might not have permission to use this network resource. contact the administratyor of this network to find out if you have permission. access is denied). However if I go into the run box on computer B & type in the folder location i wish to access on Computer A (for example, \\computer-name\folder) then the folder loads that way. Also both systems can ping each other.

As far as I can tell everything is setup correctly, im logged in as administrator, i have set each folder i share to be avaliable to everyone under the advanced sharing tab, its setup as a private network. Like I say everythings been working perfectly for several months under these settings & its only last night everything stopped working.

I use the file sharing regularly so i have to get it working properly again, having to type in the full address of the folder im trying to access isn't an ideal way of doing it.