My pc is not detecting my in built lan adapter

I have had this problem with my SysteMax Ascent as well. Not sure if you re-installed your OS or not, but the same will still apply. What is happening is that your OS (assuming Windows) is not recognizing the onboard LAN adaptor, even with it's native drivers, so the driver must be downloaded and installed. But first..

What you will need to do is open up your PC and look on your Motherboard for (what will likely be) a Letter-Number combination that will be large in size. Mine was M7NCD, yours may be different. If yours happens to be M7NCD, then your Motherboard is manufactured by BioStar, and here is their webpage with the download that you will need:
http://www.biostar-usa.com/mbdownloads.asp?model=M7NCD%20PRO
It is located under Drivers, and be sure to check to the right of the download link to find which one will be compatible with your Operating System (OS).

If it is different, enter what you see into your favorite search engine, followed by 'drivers'. You should be able to find what you're looking for in the first few results. If not, just keep checking, and if needed, use different words in your search (like lan driver, chipset). A manufacture's website is usually the best result.

Once found, check for compatible OS and install. Your LAN adaptor should work now.

Also, for good measure, check in Device Manager (Start>Right-click properties>Hardware tab>Device Manager) for any exclamation points (black ! in a yellow circle) under Network Adaptors. If there are none, then it worked! If you do see any in a different category (Sound, video, game controllers for example), look on the webpage for any drivers for that category. After I re-installed drivers for the LAN adaptor, I also had to re-install drivers for the onboard sound card as well.

Anyway, hope this helps you! It should, I had the exact same problem :D