Can no longer see shares in 'My Network Places'

Hi all,

Here is my current network config:

2 Windows 7 PCs (Home Premium)
1 Vista PC
3 Windows XP PCs
1 Netgear NAS

all in workgroup "WORKGROUP"
all assigned static IPs

Up until today every computer could see every computer on their respective My Network Places screens. The XP machines could see all the shares on the NAS and could see and connect to any other computer by just double clicking. This morning the windows 7 PCs can see each other + the Vista machine and can see the NAS listed under storage but not under 'Computer' like it used to. The XP machines can see each other but not the NAS.

Every computer can ping any other one. Any computer can type the computer name (e.g. \\NAS\share works) and that gets it temporarily instated into the network places on W7. We recently went through and assigned static IPs to every computer (before the issue). Resetting them back to DHCP isn't really an option (unless it's the only way to fix the issue, but I don't think it should be)

I've combed the net and I can't find anything that directly solves my problem. I've checked permissions, checked that simple file sharing on XP was off, checked that it's being let through firewalls, checked that file sharing was enabled in the network settings windows and a multitude of other solutions but nothing has helped me so far.

Does anyone have any solid ideas as to why this is happening and how to fix it?
Thanks in advance.

Have you looked at resetting your router?
It seems to be the common denominator.

I'll try resetting the router at the end of the work day and report back, I've been trying to avoid doing it to avoid disruption of workflow.

I have run CCleaner on my computer but none of the others, so it doesn't look like the culprit this time

Restarting the switches + router worked. I don't know if it helped, but I started the router first and let it boot completely before starting up the switches. Always the simple stuff! (I would've done it earlier but I couldn't kill peoples internet while they were working )

Thanks for your help guys, much appreciated.