I assume you are using Windows, make sure that system restore is enabled and then uninstall flash player from add/remove programs in control panel

It does sound like that may be a cause, though it could be a coincidence.

Did you have flash player on your PC before, i.e. is this an upgrade?

Have you changed any settings or installed any new software recently?

Is one end connected to your 360 right now?

It won't read that there is anything connected unless both ends are plugged into devices that are turned on

how many ethernet ports does your PC have?

If there are more than one try switching the cable to another ethernet port.

Does it say what the Ethernet cable is plugged into on a network diagram on your PC?

normally when you plug an ethernet cable into a PC a light appears. Is the power on for both the PC and the 360.

If it is and the light isn't on then it is possible that your network card has failed.

Though you may want to make sure by plugging another device into the PC using the ethernet cable.

Is there a light on at the PC connection when you plug the cable in?

Is there a light on at the 360 connection when you plug it in?

Do you have another ethernet cable which you can try?

Or something else which uses an ethernet cable which you can use to test it?

The ethernet cable shouldn't come from your PC, it should come from a router.If you plug the ethernet cable into a router and your 360 it should work correctly.

Do you have the ethernet cable plugged into a router or your PC?

Have you done a network test using your 360 to determine where the Live problem is?