Hope fully this is in the right category if not sorry.
LONG story short, some of our computers cant access the workgroup computers.

We have about 10 pc's all connected to one workgroup.
The computers have been able to detect each and every computer connected to the workgroup and they have access to each one(up until now).
But after a power cut(or in our country's terminology a load shedding occured) almost all the computers cant connect to the workgroup.
I discovered this problem trying to connect a laptop to the workgroup(it connects but cant access the workgroup computers).

The computers see the workgroup(example BUNNY) but when trying to enter it we get the following message. Workgroup not accessible... you do not have permission to access the workgroup... please call the administrator to see if you have the correct permissions(sorry it isnt complete or correct but I really want to fix this ASAP and cant be bothered to wait for the message to appear again).(NOTE - most of the pc's have administrator privileges).

I can search for the computers using search for computers near me, all the searched for computers are detected but they cant be accessed.

Nothing has changed to the network except for the power cut.
We also have a Netdrive connected(standalone) and we are all able to access and use it.
We are also able to connect to the internet.

Now I briefly searched the net for this problem but none of the problems/solutions seems to be like mine.
We have DHCP configured on the router(The pc's are connected through a series of switches which is then connected to the router) and some of the PC's have zonealarm firewall and some have windows firewall(almost all of them have avg free edition on).

My questions are these:
Is it a Router or PC problem or something else?
Do I need to change the workgroup to see if it makes a change to the problem?
And Ultimately any ideas on how to fix it?

This may be a stupid answer, but have you tried to power cycle the router?

Then try to do a ip release on all the workstations.

I'm assuming that you have DHCP on each workstation. Check that one of the routers ports haven't gone nuts.

Then try the age old method: unplug every workstation and add them back one at a time to see if one worstation causes the problem or if nothing at all works.

Then try to change out the router with another router.

Network cards are the first to go when there is a power outage. I really think your problem is a delinquent workstation.