Network bridging nightmare

[mithrandirlathspell]

Hi, first time poster, long-time tech support lurker. I've got a problem that as far as I can tell is unique, either that or my search terms aren't specific enough.

I live where I work, and so I'm connected to a semi-public network. I have a large desktop that's a custom built machine with no wireless capability, and a pretty old HP laptop with numerous mechanical failings. The two machines are linked via an ethernet cable, and up until now I've been connecting the desktop to the internet using the laptop's wifi capability through a network bridge with no problem.

Around 4 days ago, I woke up to find neither machine was connecting to the internet - I've had little blips before and took the standard steps to fix it (turning the bridge on and off, pulling and re-plugging the ethernet, restarting both machines) and got the laptop to work. I spent two days' worth of spare time fiddling with interfaces and following online guides I didn't fully understand and seemingly by a miracle with no input of my own the connection fixed itself as I was reading a debugging guide.

This morning, it went down again, and after manually assigning IP addresses and swapping out the ethernet cable and attempting to install an old wireless PCI-E adaptor I found, I've managed to get the desktop connected once more - however for whatever reason it only seems to work when I bridge the desktop's ethernet adaptor with another, unrelated adaptor. If I unbridge the connection, I am informed of an apparent IP conflict, and cannot connect.

This situation is almost fine, but I'm apparently completely unable to use my VPN client in this state and I'm concerned that it may prove unstable in the long-term.

Both machines are running Windows 7 professional, and at present the laptop has an IP which I assigned, while the desktop is using DHCP. The internet is working for both, though it seems slower than usual.

I'm happy to do whatever I need to do to get this sorted, but be warned I really don't know much at all about networking and I've very much muddled through to this point.

 

[Grobe]

Since you depict a tendency of network connection fixing itself, maybe there is very few ip addresses left on the network.
How is your desktop IP configuration? Does it have dynamic IP ? I guess the problem is that your desktop use a static IP, and therefore from time to time that specific IP address will be occupied somewhere else in the network.

 

[mithrandirlathspell]

I spoke with the guy who runs the network and he seems pretty confident that there's no imposed limits on devices. Aside from my own, there's only around 15 other devices tops connected.

My desktop is currently set to obtain it's IP address automatically, which I hope is what you're asking.

 

[mithrandirlathspell]

Done a little messing around and I've at least managed to distill the problem down a little and get rid of some unknowns.

Here is my adaptor settings when the internet is working as normal. Notice the network bridge with only 1 connected adapter.

Here's what happens when I remove said adaptor from the bridge. At this point my internet will not work.

And here's the part that's driving me to drink; the adaptor's settings are 100% identical to those of the bridge. Both are simply set to automatically acquire their IP, so I cannot fathom why one would create a conflict and one wouldn't.

I have also tried running an ipconfig with the bridge turned off, but it didn't give me any IP addresses.