Everytime I boot up my computer, I get the yellow triangle on my LAN connection, which means I can't access the internet, but as soon as I disable the network adapter then re-enable it again, it works. Not sure why it does this but it is, of course, a problem. I'm not using wireless by the way. Any suggestions?
Sounds like a quirky issue. It may be resolved by checking with the vendor and installing the latest LAN driver. However, my experience with network adapter issues that behave quirky is that you could try going into device manager, uninstalling the device, right click the computer icon, start a rescan, then check to see if the problem continues.
Do you have this trouble with any other computer on your network? Do you have a spare NIC that you can install to see if you can replicate the problem with another NIC? Sometimes, depending on the motherboard, those on-board NICs are not from reputable vendors. I've had similar issues in the past when I use to build computers. I typically stick with Intel NICs now if they are onboard.
Ok so this is a challange then. If you have already swapped out the drivers, tried uninstalling the NIC and re-installing and that hasn't worked, and you do not have any other computers to validate with, we have to assume that there is something wrong with your operating system. Some minor component that needs to be repaired.
Generally this repair is usually done by following the steps regarding device manager and drivers.
Was there ever a time that it worked fine? If so, are you able to perfrom a system restore back to that point in time?
Have you just considered the amount of time you've invested...would it be quicker just to perform a fresh install of Windows?