Vista - Vista not connecting to local web server

Dear Experts,

After running the last Windows update, I have lost access to my local web server.

Whereas, the server can not be reached via normal short-cut nor under the network directory, the server is somehow still listed as media server, ie access to media files through Windows Media player - but not as file server.

Further hereto, I tested a Cisco network setup program which managed to reconnect the access. However, when removed (only trial) the connection went down again.

My own conclusion is that Vista is blocking the access as a security measure - I just don't know where to search.

FACTS:
COMPUTER:
* Windows Vista Home Premium 32 bit, SP2
* Windows Firewall & AVG security center deactived

NAS:
* Qnap T-406 Turbo server
* DHCP, IP allocation

* Network groups identical on Computer and NAS Server "Workgroup"

Look forward to any help on how to reconnect to my server.

Best regards
Jesper Beck