Reinstalling GRUB will fix this. This question explains how:
Or if you prefer, you can use any of these methods:
If you experience any further problems booting your new Ubuntu system, please go ahead and edit your question again (then you can comment on this answer to let me know).
Everything you need to know to fix this problem is there...but in case you're interested in what is wrong and why that will fix your situation, I've included an explanation below.
The error message is actually telling you that it tried to boot via Ethernet and failed. This makes sense--to boot successfully from the fourth device in the boot list, PCI Lan, you'd have to have a boot server running on a local network.
This error message is useful to us not because it tells us it failed to boot from PCI Lan, but because it tells us it tried. That means it was unable to boot from all of the boot devices that are set before it in the list.
It makes sense that it didn't boot from USB--the Ubuntu live USB was disconnected, and you've reported that when it is connected, it boots. And it makes sense that it didn't boot from the CD/DVD drive--you probably didn't put a bootable disk in that drive.
The question is, why didn't it boot from the hard disk? We know the hard disk works, since it worked before, it worked when you installed, and you can access it from an Ubuntu live system. And it looks like the system was installed.
For the BIOS to move down on the boot device list from the hard disk, the disk must have appeared not bootable at all. That is, the problem isn't that the installed operating system begins to start and has a problem. Rather, the installed operating system cannot even start. Its boot loader, GRUB, is nowhere to be found.
While most installations go without anything going wrong, this is actually one of the more common installation problems. It can occur if you manually tell the installer not to install GRUB to the master boot record of the first hard drive, if it identifies the first hard drive incorrectly (its idea of first isn't necessarily what the BIOS tries to boot first), if it thinks a suitable boot loader is already in place (and is wrong), and possibly for other reasons.
Reinstalling the GRUB2 boot loader to the master boot record of the drive that the BIOS is trying to boot almost always solves this problem. When someone with a working Ubuntu system installs a Windows system alongside Ubuntu, the Windows installer will overwrite the master boot record with its own boot loader, which does not detect and provide an option to boot Ubuntu. That's what your situation has in common with that of users who've just installed Windows beside Ubuntu.