If your machine doesn't have a serial console, nothing any operating system can do will give you access to the PC-style BIOS messages across the serial port.
I'm not sure if I fully understand what that's trying to say. What's specifically casing trouble for me is the part between nothing and will give you. I don't think I understand how exactly it figures into the overall structure of the sentence. I suppose that we can even get rid of it and the sentence will still read well:
If your machine doesn't have a serial console, nothing will give you access to the PC-style BIOS messages across the serial port.
The original construction, however, sounds a little bit awkward to me. I could try and write my own example sentence using the exact same grammar:
Nothing that I can do will help you in this situation. Sorry, buddy, you're on your own here.
Do you think this type of phrasing is totally legitimate in English? Does it make sense grammatically and semantically to you guys? I don't know, but I do find it somewhat difficult to understand.