Vista 64 as File Server

This is my first post here, so if this is the wrong forum, feel free to move it somewhere more appropriate.

We're having some trouble with a system here at work that we're using as a file server. It's a recent model Dell Inspiron Q8200 that we're using as a QuickBooks 2009 server along with serving files for the company.

The machine is speedy and works well when it is working. The issue that we're having is that occasionally (3-4 times a week) people just can't access the shares on the system where the files are hosted. In fact, you can't even access the machine via the usual \\[servername].

The error message that pops up when you try to access the machine is as follows: "\\[servername] is not accessible. You might not have permission to use this network resource. Contact the administrator of this server to find out if you have access permissions.

The specified server cannot perform the requested operation."

Our usual fix is to reboot the server which requires that everyone make sure they aren't running QuickBooks and that no files are open which brings productivity to a halt. Very annoying. If anyone has any suggestions on how to solve this, I'm all ears.

I've googled the error message and tried several of the mentioned fixes (file permissions changes, registry changes for anonymous pw, etc) to no avail. I'm hoping that one of you may have seen this and know how to fix it so I can go back to my normal job of coding instead of playing Windows IT cleanup guy.

Exactly same issue here with i7 machine with 8G RAM, ult 64, acting as file server with 7 clients running either XP Pro, XP Home Premium, or Vista 32. Physically changed network config to reduce from 3 gigabit switches to 2, which appeared to increase time between reboots, bu problem persists.

so the file servers dont even "ping?" if that's the case there is a network configuration error somewhere. also check the power options, if this is just a pc that you guys are using as a file server, the power options should never let it go to sleep, hibernate, standby or anything like that. It should be running at full power all day.
I dont know why you guys arent just syncing the files to the server and add the share permissions from there, mapping the network drives.
But apart from that find out which port you are using to share files for this machine - the firewall in your router might prevent access to this port. you can find the port no. from running a netstat on your server or from here run TCPview from Sysinternals.com. This will also show TCP ports
http://www.sysinternals.com/Utilities/TcpView.html

if you dont have wireless connectivity and you dont allow RDP port forwarding off-site then I suggest turning off the firewall from the "file server"