Do you have a notebook or desktop with a NIC that supports VLAN tags? If so, I would plug a notebook directly into the ASA with a VLAN tag of 4 and machine sure you can access the Internet. This will verify the NAT and access-rules on the ASA allow that VLAN to get to the Internet.
I believe your tagging and trunking configuration are correct. I am more suspicious that the ASA is now allowing the traffic out.
On the MS does the local status page give any reason? For example, does it say it has a DNS problem, or a default gateway problem, etc?